Frogs face fatal fungal foes

Pathogens are organisms that cause disease, and like all organisms, they obey evolutionary principles. Pathogens that survive and reproduce successfully in a particular environment will have more offspring than those that are less successful, thereby passing on those traits that promote successful reproduction to future generations. The problem is that many pathogens change their environment in a way that makes their environment less hospitable for their own survival or reproduction. For example, the fungal pathogen Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis in its amphibian host, which may severely reduce the host population size to the point where few individuals survive. If the host population goes extinct, then there are no hosts for the fungal offspring to infect.

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Scanning electron micrograph of Batrachochytrium denbdrobatidis spore. Credit: Dr. Alex Hyatt, CSIRO Livestock Industries’ Australian Animal Health Laboratory.

Fortunately for Bd, but unfortunately for amphibians, there are several ways out of this conundrum. One approach is a reduction in pathogenicity so that a pathogen’s host species is able to tolerate the infection (and of course, natural selection will at the same time favor an increase in the host species’ tolerance for the pathogen). A second approach is to broadcast a wide net by infecting many different species. That way if one host species goes extinct, there are always many other species to infect. Bd infects over 500 species of amphibians, and has been implicated in the extinction of over 100 amphibian species, and the severe decline of an additional 100 species.

Ben Scheele and his colleagues wanted to know why the endangered northern corroboree frog, Pseudophryne pengilleyi, was declining in southeastern Australia. Several previous studies showed that many corroboree frog populations declined or went extinct in that region over the past 20 years, while the abundant common eastern froglet, Crinia signifera, showed no signs of decline over the same time period. Pilot studies showed that eastern froglets were heavily and commonly infected with Bd. The researchers reasoned that eastern froglets could be acting as a reservoir for Bd, so that corroboree frog populations are being decimated by association with Bd-infected eastern froglets.

Female Ppen copy Hunter

Female Pseudophryne pengilleyi. Credit: David Hunter.

Preliminary surveys indicated that the decline of corroboree frogs was not uniform across the study site; in fact there were some newly discovered populations that were doing very well. The researchers defined three types of sites in their research area. Absent sites (40 in total) had corroboree frogs in 1998, but the population went extinct by 2012. Declined sites (17 in total) had a greater than 80% decrease in abundance since 2000. New sites (25 in total) were newly discovered since 2012, and had much higher population densities than declined sites.

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Study area in southeastern Australia, showing locations of Absent, Declined and New sites.

Unfortunately, it is impossible to visually distinguish an infected frog from an uninfected frog, at least until the few hours before death. But the researchers needed to be able to tell if a frog had chytridiomycosis. So they collected skin swabs from the frogs during the breeding season – only working at night to ensure cool humid conditions which minimized frog stress. They then did real time PCR on these samples to quantify the intensity of Bd infection.

Scheele and his colleagues had three important questions they were now prepared to answer. First, how prevalent is Bd in these two species? They found that infection rate was much higher in eastern froglets (79.4%) than in corroboree frogs (27.3%). The intensity of infection (measured by the number of fungal spores) was also much greater in eastern froglets than in corroboree frogs.

Second, do eastern froglets act as a reservoir for Bd, leading to infection and decline of corroboree frog populations? As we discussed earlier, the two species coexist at some sites, but not at others. If eastern froglets act as a reservoir for Bd, we would expect corroboree frogs to have higher infection rates at sites they share with eastern froglets, than they do at sites without eastern froglets. In support of this prediction, Bd prevalence in corroboree frogs was 41.4% at sites with eastern froglets, but only 2.6% at sites with no eastern froglets.

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C. signifera (left) and P. pengilleyi spending quality time together in a P. pengilleyi nest. Credit: David Hunter.

Finally, the researchers want to identify conditions that will promote corroboree frog recovery. They approached this quantitatively by modeling the probability of a site being classified as Absent, Declined or New, in relation to eastern froglet abundance. Based on their survey data of 81 sites, those sites with the highest eastern froglet abundance are most likely to be classified as Absent (corroboree frog extinction), while sites with very few eastern froglets are most likely to be classified as New (thriving corroboree frog populations).

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Probability of a site being classified as Absent, Declined or New, based on eastern froglet abundance. Data are log transformed. Dashed lines are 95% confidence intervals.

Scheele and his colleagues conclude that eastern froglets are a reservoir host for Bd, and have played a major role in the decline in corroboree frog populations. The researchers point out that, in general, areas lacking reservoir hosts may provide endangered species with refugia from infectious disease. For managing endangered species, conservation biologists should carefully monitor sites for the presence of reservoir hosts so they don’t reintroduce rare and endangered animals into locations where they will be attacked and killed by pathogens.

note: the paper that describes this research is from the journal Conservation Biology. The reference is Scheele, Ben C., David A. Hunter, Laura A. Brannelly, Lee F. Skerratt, and Don A. Driscoll. “Reservoir‐host amplification of disease impact in an endangered amphibian.” Conservation Biology 31, no. 3 (2017): 592-600. Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.

Golden Eagles: no tilting at windmills

Todd Katzner and several other scientists were puzzled by a vexing problem. They knew that the wind turbines at Altamont Pass Wind Resource Area (APWRA) were killing large numbers of Golden Eagles that flew into their spinning blades. Yet the population of Golden Eagles in the area had stayed relatively stable over the years despite this unnatural source of mortality. The researchers considered two possibilities. First, this population of eagles may have had unusually high birth rates or unusually low death rates from other sources to compensate for the high windmill-induced mortality. Alternatively, immigrant Golden Eagles might be replacing those killed by turbines.

Altamont Pass Wind Farm

Altamont Pass Wind Farm, California. Credit: Todd Katzner.

This question has important implications for conservation biologists. If immigrant Golden Eagles are replacing those killed by windmills at APWRA, then the apparent stability of the local Golden Eagle population may be at the expense of other populations that are providing APWRA with these immigrants. So, even though APWRA’s windmills are not directly causing local eagle populations to decline, windmills at APWRA (and other windmill sites) may be indirectly leading to a decline in other populations. So Katzner and his colleagues did genetic and molecular analyses of tissues remaining from these killed eagles to learn as much as they could about these eagles and where they came from.

Golden Eagle in flight

Golden Eagle in flight. Credit: Michael J. Lanzone.

The researchers used tissue samples from 67 eagles that were killed at APWRA between 2012-2014. They subjected these tissues to a variety of genetic tests to determine the sex and age of each individual, and to evaluate the genetic differences between individuals killed by the windmills.

In addition, Katzner and his colleagues used stable isotope analysis to evaluate whether the killed individuals were local birds, or immigrants from afar. For this analysis the stable isotope ratio is the ratio of a rare and nonradioactive isotope of hydrogen (2H) found in the sample (feathers of killed birds) in relation to the common isotope (1H). A feather’s stable isotope ratio is very tightly correlated to the stable isotope ratio of the water the bird drinks. The last important point is that different regions of the world have different characteristic stable isotope ratios in rainwater. So if you can determine the stable isotope ratio of a bird’s feather, you can compare it to the world stable isotope ratio map, and determine where the bird most likely spent the previous year (once birds molt, their new feathers assume the stable isotope ratio of their new location). This approach will underestimate the number of immigrants, because some distant locales have a similar stable isotope ratio as APWRA, and birds from those regions will be incorrectly scored as being local.

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Map of May-August stable isotope ratios (of 2H in rainwater).  Same colors represent similar stable isotope ratios, ranging from relatively high ratios (deep orange), to relatively low ratios (dark blue). I don’t discuss the meaning of the circles and triangles in this blog post.

Based on this analysis, more than 25% of the dead eagles were immigrants to the area, with some birds originating from more than 800 km away. The researchers point out that APWRA might be particularly attractive to eagles looking for a home because it provides two types of resources that are important to these birds – visually open feeding grounds with easily-located prey, and a consistent updraft to facilitate relatively effortless flight.

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Probability that an eagle killed at APWRA was local.  If the probability was less than 0.5 the researchers scored it as immigrant; if greater than 0.5 the researchers scored it as local.

About half of the immigrants that could be sexed were juveniles or subadults. The researchers argue that the apparent stability of the population in the APWRA region is achieved by young immigrants replacing those birds that are killed by windmills.

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Percentage of local vs. immigrant (nonlocal) Golden Eagles by age.

Katzner and his colleagues are concerned that APWRA functions as an ecological sink that attracts eagles, primarily from nearby western states, to replace those killed by windmills. High death rates are particularly problematic to slow-growing populations, such as Golden Eagles, which usually lay only two eggs, with generally only one surviving chick per breeding season (the larger chick often kills its sibling). The researchers also point out that windmills also kill many other animals, including numerous bat species, which also have slow-growing populations. They encourage the renewable-energy industry to develop technology that will reduce windmill-induced death. Such efforts are already underway, and there is preliminary evidence that newer generation turbines are reducing Golden Eagle mortality rates.

note: the paper that describes this research is from the journal Conservation Biology. The reference is Katzner, T.E., Nelson, D.M., Braham, M.A., Doyle, J.M., Fernandez, N.B., Duerr, A.E., Bloom, P.H., Fitzpatrick, M.C., Miller, T.A., Culver, R.C. and Braswell, L., 2017. Golden Eagle fatalities and the continental‐scale consequences of local wind‐energy generation. Conservation Biology31(2): 406-415.Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.

Fungal fiasco for furry flying friends

Because they are nocturnal, relatively quiet (to our ears), and in general, not very large, most people don’t realize how abundant and diverse bats are. Bats make up about 20% of all mammal species. They are ecologically critical in their roles as insect predators, pollinators and seed dispersers. Unfortunately, bats in the eastern United States and Canada are under siege by the fungus Pseudogymnoascus destructans (Pd), which has killed several million bats in the eastern United States and Canada since its emergence in 2006.

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Bats hibernating in Aeolus Cave (Vermont) in 2009, prior to fungal induced die-off. Credit: Joel Flewelling.

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The same location one year later. Credit: Joel Flewelling.

Bats are infected when they return to their caves and mines to hibernate. The fungus invades their skin, creating white fungal patches on the muzzle and ears, and disrupting hibernation patterns with consequent high overwintering mortality for several species. The disease is called white-nose syndrome (WNS)

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Two little brown bats (Myotis lucifugous) with white-nose syndrome. Credit: Alan C. Hicks.

Winifred Frick has been studying bats for 17 years. She and her colleagues are trying to determine the long-term prognosis for WNS in North American bat populations. They are interested in several related questions. First, how is WNS spreading in North America? Second, are some individuals, or species, tolerant of the fungus, and thus able to sustain infections without dying? Third, is there any evidence for the evolution of resistance, in which some individuals can fight off the infection, and thus carry reduced fungal loads?

Thirty ecologists and even more research assistants throughout the United States and Canada collaborated in this study, collecting tissue from many thousands of bats, and suspected fungal samples from 79 cave walls. This team of researchers used molecular biology techniques (quantitative PCR) to estimate fungal loads. The map and data below summarize some of the findings.

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The map on the left shows the spread of WNS over the past 9 years (see key below map). The eight graphs show colony size in red, using the left y-axis, and Pd load in log10 attograms (1 attogram (ag) = 10-18grams), using the right y-axis. Thus, for example, a Pd load value of 5 = 100,000 ag, while a Pd load value of 4 = 10,000 ag.

The first point is that WNS was first detected in New York (black patch with arrow # 1), and quickly spread throughout the Appalachian Mountains in New England, north into Canada, and south into Virginia and West Virginia. More recently WNS has spread further west, and most disturbingly (not pictured) it was also found in the state of Washington in 2016.

On a slightly brighter note, populations of two species, Myotis lucifugus and Perimyotis subflavus, are showing evidence of resistance. For example, two Myotis lucifugus populations (1 and 2 on the map and graph) have reversed their initial sharp declines and are showing significant recovery (red dots). While all sampled individuals still have numerous Pd parasites (open circles on the graphs), the average fungal load has dropped sharply in several populations in recent years (blue dots), indicating the development of resistance.

But there is still a huge reason for concern. For example, consider the northern long-eared bat, Myotis septentrionalis.  WNS spreads very rapidly and fungal loads climb to unsustainable levels among individuals of this species, usually leading to complete extirpation within three years of the first Pd infection at any site. This bat has disappeared from 69% of its caves, and is now endangered in Canada, and is being considered for protection under the United States endangered species act.

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Lone Myotis septentrionalis with WNS. Credit: Alan C. Hicks.

The question becomes, what can we do about white-nose syndrome? This disease is particularly pernicious, because samples from cave walls indicate that the fungus can persist outside the host for extended periods of time. So even if populations crash, there is still a reservoir of infection waiting to attack any bats that might move into a cave. Frick suggests that we need to think broadly about conservation efforts that might help the bats, particularly in areas where they are developing tolerance or resistance. She recommends identifying and protecting habitat that contains suitable hibernacula during the winter, and rich foraging sites and appropriate roosts for the rest of the year.

note: the paper that describes this research is from the journal Ecology. The reference is Frick, Winifred F., Tina L. Cheng, Kate E. Langwig, Joseph R. Hoyt, Amanda F. Janicki, Katy L. Parise, Jeffrey T. Foster, and A. Marm Kilpatrick (2017). Pathogen dynamics during invasion and establishment of white‐nose syndrome explain mechanisms of host persistence. Ecology 98(3): 624-631.Thanks to the Ecological Society of America for allowing me to use figures from the paper. Copyright © 2017 by the Ecological Society of America. All rights reserved.

Timely trophic cascades

While many of us appreciate oysters as delectable delights, we may underestimate the environmental benefits they also bring to the table. As filter feeders, they remove vast quantities of organic debris from the water, and as reef builders they protect our shorelines from violent wave action.

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Oyster reef. Credit: WFSU, Public Media

Of course, humans are not the only animals to enjoy eating oysters. For example, along portions of the Florida coast dominated by the reef-building oyster Crassostrea virganica, the mud crab, Panopeus herbstii, is a major consumer of juvenile oysters. In some locations, the average abundance of these voracious crabs can exceed 10 adults/m2 of reef. But all is not food and gravy for these crabs, as lurking in nearby burrows are equally voracious crab-eating toadfish, Opsanus tau. When toadfish are detected, the mud crabs will hide within the protective matrix of oyster shells and sediment that form the reef.

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A mud crab hiding among a cluster of oysters. Credit: WFSU, Public Media

By consuming mud crabs, toadfish are indirectly protecting oysters from being eaten. Ecologists call this a consumptive effect (CE). But David Kimbro and his colleagues have also shown than toadfish, by their mere presence, can also protect oysters by scaring the crabs into hiding. Since, in this case, they are not consuming the crabs, ecologists call this a non-consumptive effect (NCE). Together, CEs and NCEs should both increase oyster survival. More surviving oysters lead to higher overall feeding by oysters, which lead to more oyster poop, and more organic matter deposited into the sediment below. Ecologists call this type of relationship a trophic cascade, because the effects on one species cascades down through the ecosystem. In this case, increasing toadfish will decrease crabs, thereby increasing oysters and sediment organic matter. Conversely, decreasing toadfish should increase crabs, thereby decreasing oysters and sediment organic matter.

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Toadfish/mud crab/oyster/sediment organic matter (SOM) cascade. Dotted arrows are indirect effects

Kimbro and his colleagues wanted to explore this trophic cascade in more detail. They set up an experiment with 24 artificial reefs (made out of natural materials, except for the surrounding fence), which included 35 L of live oysters. They supplied each reef with 0, 2, 4, 6, 8 or 10 live crabs, and provided half of the reefs with a caged toadfish. They then measured oyster survivorship in relation to crab density in the presence or absence of predators.

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Setting up an artificial reef. Credit: WFSU, Public Media

The graphs below summarize their findings. The first thing to notice is that mud crabs were bad news for oysters, as survivorship plummeted when mud crabs were abundant. However, early in the experiment (graphs A and B) having a toadfish around helped out considerably. Oysters survived much better in the presence of toadfish (triangles and dotted curve) than they did without toadfish (circles and solid curve). But by the middle of the experiment (Graphs C and D), the toadfish no longer helped. Interestingly, by the end of the experiment (Graph E) the toadfish was once again helping the oyster’s cause, as survivorship was again greater in the presence of toadfish than in its absence. Realize that the difference between the dotted and solid curve is a measure of the NCE, as the toadfish are not eating the crabs (because they are caged). So we can conclude that there was a strong NCE early on, which waned in the middle of the experiment and then returned by the end of the experiment.

Kimbrograph

A second finding is that the reef grew (expanded) when there were no crabs present, but that even two crabs were enough to reduce reef growth to zero. In addition sediment organic matter was greatest when there were either none or only two crabs present in the reef. Four or more crabs in the reef reduced the deposition of sediment organic matter. These findings were not influenced by the presence or absence of toadfish.

This is a complicated system, but we (and toadfish, crabs and oysters) live in a complicated world. And there are several other complications that I have not even mentioned! We might argue that the crabs may habituate (get accustomed) to these toadfish, so that by the middle of the experiment, the toadfish NCE had worn off. That begs the question of why the NCE returned towards the end of the experiment. Kimbro suggests that at the beginning of the experiment, the novelty of the predator cue probably caused strong NCEs. But by the middle of the experiment, the crabs became hungry and chose to forage regardless of predator cue. Finally, towards the end of the experiment, the crabs, having filled up on juvenile oysters, opted to hide rather than forage when toadfish were present. Whatever the reason, these findings caution us that if we want to understand trophic cascades, we need to consider the dimensions of both space and time.

note: the paper that describes this research is from the journal Ecology. The reference is Kimbro, D. L., Grabowski, J. H., Hughes, A. R., Piehler, M. F., & White, J. W. (2017). Nonconsumptive effects of a predator weaken then rebound over time. Ecology 98(3): 656-667. Thanks to the Ecological Society of America for allowing me to use figures from the paper. Copyright © 2017 by the Ecological Society of America. All rights reserved.

E-lek-trical death to migrants

Leks have been described as singles bars for birds, though with all the singing and dancing that can go on there, a Karaoke bar might be the closest human analog. Male birds, such as the Great Bustard, Otis tarda, get together at traditional display grounds (leks) and strut their stuff, providing no material resources for females, and being visited by females solely for the purpose of mating.

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Three male Great Bustards on a lek in Central Spain. Credit: Carlos Palacin.

After the mating season concludes, some male great bustards in central Spain fly further north while others remain near the lek area. Migrants benefit from cooler and moister environmental conditions, and, in some cases, greater food availability. But migrants flying to a new area consume calories, and more recently, run the risk of flying into power lines, thereby injuring or killing themselves.

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Newly erected power lines in central Spain. Credit: Carlos Palacin.

 

Carlos Palacín and three other researchers used radio-tracking technology to follow the behavior of 180 male bustards over the course of 16 years. They knew that some bustards died from collision with power lines, but they didn’t know whether these collisions were affecting migrants and non-migrants (sedentary birds) differently, nor if these collisions were changing the migratory behavior of bustards in the 29 breeding groups they studied. So they tracked their birds by ground and by air and determined whether each bird was migrant or sedentary, how long each bird survived, and when possible, the cause of death. For migrant bustards, the researchers measured when and where they migrated, and whether they remained migrants their entire lives.

Palacín and his colleagues discovered that birds migrated away from the lek primarily in May and June, and returned to the breeding grounds over a much more prolonged time period during the autumn and winter.

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About 35% of the birds were sedentary, while 65% migrated an average of 89.9 km, with the longest migration of 261 km. Migrants had much higher mortality rates; for example among 73 birds captured and marked as juveniles, migrants survived an average of 90.6 months (post marking), while sedentary males survived an average of 134.7 months, almost 50% longer! The same pattern follows for 107 birds that were captured and marked as adults. The lesson here is that migration kills.

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So why migrate? Well it appears that before humans (and in particular, before power lines), migration was a much more beneficial strategy. The researchers identified three causes of bustard mortality: collision with power lines in 37.6% of the cases, poaching (9.1%) and collision with fences (2.6%). The bustard forensic team was unable to determine mortality in the remaining cases, so these percentages may underestimate human impact. Importantly, the researchers discovered that death from power lines was more than three times greater in migrants than in sedentary birds.

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This study clearly demonstrates that human infrastructure can shape the migratory behavior of a population. Over the time period of the study, the percentage of sedentary birds has increased sharply even though food availability actually decreased near the breeding grounds as a result of urbanization.

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The decrease in migration may be compounded by a finding that juveniles learn to migrate (or not) from adults during their first three years of life. So if there are more sedentary adults to serve as role models for juvenile behavior, more juveniles will develop into sedentary adults. But sedentary behavior can have several drawbacks. A greater number of sedentary males will increase competition for food and other resources. Also, birds may overheat during particularly hot summers near the breeding grounds. In addition, sedentary birds may have higher inbreeding rates and lower genetic diversity, which in turn can make a local population more susceptible to disease and other environmental changes, ultimately making it more prone to extinction.

note: the paper that describes this research is from the journal Conservation Biology. The reference is Palacín, C., Alonso, J. C., Martín, C. A., & Alonso, J. A. (2017). Changes in bird‐migration patterns associated with human‐induced mortality. Conservation Biology 31: 106-115Thanks to the Society for Conservation Biology for allowing me to use figures from the paper. Copyright © 2017 by the Society for Conservation Biology. All rights reserved.

Climate change at loggerheads

In the late 16th century, “logger” referred to a large block of wood, so a loggerhead would describe a large and presumably hard head. Whether loggerhead turtles got their names from this source is not clear, but it is true that they are endowed with unusually large heads and powerful jaws that are ideal for crushing shellfish such as crabs, whelks, clams and mussels. Though they are still relatively abundant, many populations worldwide are declining, and listed as near threatened, vulnerable or endangered.

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credit: Jaymie Reneker

Conservation biologists classify species in accordance to their probability of going extinct. The table below shows the classification definitions used by the International Union for Conservation of Nature (IUCN).

Extinct No known individuals remaining
Extinct in the wild Only survivors in captivity or outside their naturalized range
Critically endangered Extremely high risk of extinction in the wild
Endangered High risk of extinction in the wild
Vulnerable High risk of endangerment in the wild
Near threatened Likely to become endangered in the near future
Least Concern Species is widespread and abundant

The future survival of loggerhead turtles demands a concerted effort by humans to preserve nesting habitat along coastlines, and to avoid catching them in gill nets and longlines that are intended for other species. Hatchlings, usually about 100 per nest, are particularly vulnerable, and will move very rapidly from their nest along the beach into the water, and swim away from the shoreline without resting for several days. Most don’t make it, becoming dinner for many different predators, including a variety of shorebirds. Those that survive may, later in their lives, migrate over 12,000 km between nesting beaches and feeding grounds.

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credit both photos: Jaymie Reneker

As an undergraduate at Iowa State University, Jaymie Reneker worked with Dr. Fred Janzen on painted turtles along the Mississippi River. Janzen was interested in how climate change might affect sexual determination in his turtles, so when Reneker moved to the University of North Carolina to do Master’s research on loggerhead turtles with Dr. Stephanie Kamel, she wanted to know how climate change might be affecting sexual determination  in loggerheads. Reneker and Kamel knew from several previous studies that sex in loggerheads is determined by the egg temperature during the middle third of the approximately 60-day incubation period. In their study area on Bald Head Island off the North Carolina coast, eggs incubated above 30 ° C were primarily female, while eggs incubated below 28 ° C were primarily male. Females bury their eggs in the sand, and leave them to incubate on their own, so egg temperature is strongly influenced by the temperature of the surrounding sand.

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credit: Jaymie Reneker

Egg temperature also determines how rapidly the eggs develop, with the result that rapidly developing eggs are primarily female, and slowly developing eggs are primarily male. This relationship is very useful, because as a threatened species, the researchers were legally barred from any actions that might harm the hatchlings. So they used the interval between egg laying and hatching (incubation duration) as a proxy, or substitute, for actual measures of sex-ratio (sex of loggerhead hatchlings can only be determined by highly invasive techniques).

Reneker and Kamel reasoned that climate change over the past 25 years would be associated with increased air temperature, increased sand temperature, shorter incubation duration, and thus a more female-biased sex ratio. The Bald Head Island Conservancy has monitored loggerhead nests since 1991 by patrolling the beaches with trained teams of observers every night during the nesting season, and surrounding each nest with a metal cage to protect it from predators. Temperature data were collected from a nearby weather station. Lastly, Reneker and Kamel estimated sex ratios using data from several earlier studies that correlated incubation duration with actual sex determination based on gonadal dissection of individual hatchlings.

The researchers discovered that air temperature has increased almost 2 ° C between 1991 and 2015 at Bald Head Island.

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During that same time period, mean incubation duration has decreased about 7 days, leading to a sharp increase in the estimated % female hatchlings from about 40% to almost 70%. While Reneker and Kamel expected a decrease in incubation duration, they were startled to observe such a dramatic decrease.

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The researchers point out that global temperatures are expected to increase substantially over the next century, which they fear may lead to a continued and more pronounced feminization of this species. Over time, there may simply not be enough males around to fertilize all of the eggs. If this happens, the loggerhead turtle populations may become more critically endangered, and on the road to extinction.

note: the paper that describes this research is from the journal Ecology. The reference is Reneker, J. L., and S. J. Kamel. “Climate change increases the production of female hatchlings at a northern sea turtle rookery.” Ecology 97.12 (2016): 3257-3264. Thanks to the Ecological Society of America for allowing me to use figures from the paper. Copyright © 2016 by the Ecological Society of America. All rights reserved.