Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles

Summary: A study done by J. Roger Brothers and Kenneth J. Lohmann on loggerhead sea turtles analyzed a 19 year database of nesting sites for the 12 counties along the east coast of Florida to determine if geomagnetic imprinting was used to return to natal beaches.

Natal homing is a pattern of behavior in which animals migrate away from their geographic area of origin and then return to reproduce in the same location where they were hatched. Loggerhead sea turtles are an extreme case of this. They travel long distances from the beaches they were born, on only to return regularly to nest. Not much is known about how this occurs.

One hypothesis is that turtles imprint on the unique geomagnetic signature of the beach they hatched on and use it to come back. Earth’s magnetic field changes over time the period of time the turtles are away so geomagnetic imprinting should cause turtles to change their nesting locations as magnetic signatures drift slightly causing either longer or shorter nesting spaces along the coastline. 

A convergence index was created to quantify the degree of movement within each county. Analysis of the relationship between each convergence index and nesting densities from the 19 year data base confirmed the predictions of geomagnetic imprinting. The highest convergence indices were associated with the largest nesting densities. Divergence was also associated with low nesting densities. This was true for all 12 counties. 

A similar study done with salmon showed the destination was the same regardless of route, whereas this study shows a change in endpoint due to change in magnetic fields.

These findings confirm and provide strongest evidence to date that sea turtles imprint on the geomagnetic signature of their natal beaches and use it return. The results also confirm the findings of geomagnetic imprinting in salmon and suggest that it is used in natal homing for other animals. 

Citation: Brothers. J.R., Lohmann K.J., 2015. Evidence for Geomagnetic Imprinting and Magnetic Navigation in the Natal Homing of Sea Turtles, Current Biology, Vol. 25. pg 392-396

Freezing and Switching Environments: Testing Local Adaptation of Microbes in Water to Variation in Time and Space

Date Published:  November 20, 2014

Source: Evolution: International Journal of Evolution

Summary:  After freezing isolated microbes of several genera at different times and placing them in each other’s environments, no significant pattern of growth of the microbes depending on chemical balances in the water was detected while bacteria grew slower in their home environments after being frozen for longer periods of time. 

The purpose of the study is to see if organisms are more fit in their native environments due to local adaptations, or similar but foreign environments with slight changes in the biotic and abiotic factors.  This is interesting because one would expect this to be true since natural selection causes populations of organisms to be specifically adapted to their environment.  

In this study, water from 6 different lakes and ponds in Canada was collected.  The aquatic microbes present in the water were isolated, cultured, and frozen.  The chemical balance in each of the water samples (including several elements such as sodium, calcium, magnesium, and potassium) collected was recorded and the water was filtered and frozen as well. Since the microbes and water chemistry was preserved at the time, the thawing of them later on is like having them travel forward in time. 

After, the bacteria that had been isolated was put in each of the different water samples from the different lakes.  
The results showed that bacteria grew more slowly in their native water than in foreign water. Also, results showed that older samples of bacteria grew slower than newer samples.  The water chemistry also did not affect the pattern of growth of the bacteria.  
These results are quite surprising since they are almost opposite of the expected results (it was expected that bacteria would grow faster in their  native environments due to local adaptations).  However, the bacteria were still adapted better to some of the of the 6 environments relative to the others probably due to ideal chemical conditions, although results were inconsistent. 

Citation: Fox, J. W. and Harder, L. D. (2015), Using a “time machine” to test for local adaptation of aquatic microbes to temporal and spatial environmental variation. Evolution, 69: 136–145. doi:10.1111/evo.12543

Adaptations of Aegean Wall Lizards to the Trade-Off Between Natural and Sexual Selection

Date of Publication: July 28th, 2014

Source: Behavioral Ecology

Summary: A study was conducted to investigate whether or not the coloration of Aegean wall lizards has adapted to accommodate the trade-off that exists between highly conspicuous sexual signals and detection avoidance by predators.

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There currently exists a potentially threatening trade-off between natural and sexual selection in animals. Many animals use sexual signals to attract mates and ward off competition, but all animals are in need of camouflage from predators. This study by Marshall and Stevens of the University of Cambridge's Department of Zoology examines how animals -- in particular, the Aegean wall lizard -- have adapted for this trade-off. Research has shown that conspicuous sexual signals are located on the surfaces of the animals that are in view of their potential mates and rivals (conspecifics), while out of view of predators; at the same time, camouflage is found heavily on the surfaces of animals that are more exposed to their predators' sights. This phenomenon is known as "signal partitioning". The authors of this journal article hypothesized that Aegean wall lizards exemplify signal partitioning; specifically, sexually competing males would be more conspicuous than females to both potential mates/rivals and predators, with camouflaged backs and brightly colored sides, while females would be camouflaged entirely (known as sexual dichromatism).

To test their hypotheses, Marshall and Stevens measured the conspicuousness of 83 wall lizards from three different islands as compared to their natural backgrounds using digital imaging of three regions of the lizards' bodies: ventrolateral flanks, upper backs, and lower backs (see left). They then tested for differences in the perceptions of avian predators and conspecifics of the lizards' coloration and conspicuousness. This was done by converting the pictures of the lizards that were taken on-site into images that would be seen if the camera was actually an avian predator and if the camera was a conspecific. To determine how well lizards blended into their environment/how conspicuous they were from the points of view of an avian predator and a conspecific, the researchers quantified the contrasts between the examined body parts of the photographed lizards and their background environment.

There were several notable results of the performed experiment. For one, the two parts of the lizards' bodies (the part visible to avian predators and the part visible to conspecifics) were distinct in coloration. Moreover, the coloration of the ventrolateral flanks was more distinct from the lizards' backgrounds than the coloration of the upper and lower backs, which supported the initial part of the researcher's hypothesis. In particular, Marshall and Stevens found that males were more conspicuous in coloration on the upper back and flanks, but not on the lower back, suggesting that the flanks and upper back are sexually dichromatic signals in wall lizards. In further support of their hypothesis, the researchers also found that females were inconspicuous throughout all three observed regions of the body, while males had significantly more conspicuous ventrolateral flanks than upper and lower backs.

In conclusion, Marshall and Stevens found much support for their hypothesis concerning the adaptation of Aegean wall lizards to the trade-off between natural and sexual selection. Their findings can be generalized to many animals, in which this signal partitioning adaptation exists, pinpointing one of the great phenomena of evolutionary history.

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Citation:

Marshall, K.L.A. and Stevens, M. 2014. Wall lizards display conspicuous signals to conspecifics and reduce detection by avian predators. Behavioral Ecology 25(6), 1325–1337

Competing Natural and Sexual Selection: Variation in the Visual Signals of Wall Lizards

Date published: July 28, 2014

Source: Behavioral Ecology

Summary: A study suggests that coloration and conspicuousness of wall lizards evolved under conflicting demands of natural and sexual selection.

            A study suggests that coloration and conspicuousness of wall lizards evolved under conflicting demands of natural and sexual selection, according to a study published in 2014 by Kate Marshall and Martin Stevens from the University of Cambridge in the journal Behavioral Ecology.

            Three populations of Aegean wall lizards were studied from the islands of Skopelos, Syros, and Foelgandros. The authors investigated four main points: whether the lizards were more conspicuous to conspecifics (members of the same species) than to predators, if males were more conspicuous than females as a result of sexual competition, if there was variation in visual signals between different parts of the body, and whether the conspicuousness of the lizards differed among the three populations. Lizards must be noticeable enough to attract potential mates but they must also remain somewhat camouflaged to avoid detection by predators, resulting in conflicting natural and sexual selection.

            The results showed that lizards were more noticeable to conspecifics than to avian predators across all body regions in all three populations. Avian predators can only perceive relatively high wavelengths of UV light while lizards can perceive a much higher range. The increased conspicuousness to conspecifics was caused in part by the use of short UV wavelengths to remain noticeable to potential mates yet avoid detection by predators.

            In the Skopelos population, males exhibited increased conspicuousness over females, but in the Syros population, both males and females displayed higher conspicuousness of certain body regions. The Syros population has a higher population density, which can lead to increased sexual competition, even for females, resulting in the need for both males and females to attract mates. This is indicative of evolution because the conspicuousness varied among populations to best suit the needs of the lizards.

            It was also shown that there was variation in conspicuousness between body parts of the lizards. In the Skopelos and Syros populations, the flanks of the lizards were more conspicuous than the backs. Avian predators view the lizards from above, so their backs were more camouflaged, and because potential mates view the lizards from the side on the ground, the sides of the lizards were more noticeable.

             The Foelgandros population of lizards did not exhibit the significant differences in conspicuousness between body parts that was found in the other two populations. This is likely because the Foelgandros island lacks a number of the avian predators that are on the other islands, so the lizards have a lower risk of detection and therefore less of a need for camouflaged backs.

            The findings of the study indicate that the coloration of the lizards has evolved to make the lizards better suited to their environment. The competing demands of natural selection, which would make the lizards less noticeable to their predators, and sexual selection, which would result in lizards being more conspicuous to potential mates, led to different conspicuousness between certain body regions and differences between males and females. These differences are indicative of evolution.

Journal Reference:

Marshall, K.L.A, and Stevens, M. 2014. Wall lizards display conspicuous signals to conspecifics and reduce detection by avian predators. Behavioral Ecology 25: 1325-1337.

How did the SWS2 Gene Evolve?

Date Accepted: November 19,2014

Source: Wiley Online Library

Institutions Involved: Department of Ecology & Evolution, University of Chicago, Departments of Ecology & Evolutionary Biology, Cell & Systems Biology, University of Toronto, Centre for the Analysis of Genome Evolution & Function University of Toronto,

Summary: Researchers try and find out if color perception in birds had an influence on the evolution of a gene that controls feather color.

Did you ever wonder why some birds have bright feathers while others do not? The researchers from the University of Chicago and the University of Toronto had a similar question. Natasha Bloch, James Morrow, Belinda Change, and Trevor Price wondered, "Why did the Old World warblers have fewer pigmented feathers in comparison to the New World warblers?" So, they decided to conduct an experiment to find out. This particular experiment happens to be interesting because the researchers attempt to find out how the SWS2 gene (which codes for pigment) evolved.

This happens to be the cladogram from the paper. Here, you can see what is referred to as the Old World Warblers and what is referred to as the New World Warblers.

 For this experiment the researchers had three hypotheses. Their null hypothesis stated that the SWS2 gene remained unchanged during the course of evolution. The other two hypotheses each describe different ideas of how the SWS2 gene could have evolved. The first hypothesis believes that the gene is similar in both the New World and Old World Warblers, but was different in their respective anscestors; it also suggests that this difference in color is due to the environment of each of the birds. The second hypothesis states that the gene shifted as the New World Warblers diverged from Old World warblers, but they passed through another ancestor that occupied a different environment, which then lead to the different color perception and color difference in the feathers of each set of birds. This last hypothesis happened to be the researchers' most favored idea.

The researchers tested their ideas by sequencing the SWS2 gene from both of the warbler clades and also from some outgroups. For the New World warblers, the researchers collected birds that died from building collisions during migration in Chicago. For the Old World warblers, they used RNA samples. Once the researchers had  sequenced all of the SWS2 genes from various birs, they then reconstructed the SWS2 sequence evolution. They also identified all the variants with at least one substitution as candidates for shifts in color perception.They found that despite having 6 differences in the amino acid sequences, the ancestors of both

warbler clades had similar color perception.

In conclusion, they found that the color perception of the ancestors of both the New World warblers and the Old World warblers were the same, so this could not have contributed to the evolution (color variation) in the New World warbler's feathers. The researchers say that when they do figure out what the reason for behind the adaptiation is, they will then be easily able to determine if this evolved trait is due to historical  contingency or not.

Journal Reference: Bloch, N. I., Morrow, J. M., Chang, B. S. W. and Price, T. D. (2015), SWS2 visual pigment evolution as a test of historically contingent patterns of plumage color evolution in warblers. Evolution, 69: 341–356. doi: 10.1111/evo.12572

The Evolutionary Response to Unpredictable Environmental Change

Date Published: November 24, 2014

Source: Proceedings of the National Academy of Sciences (PNAS)

Institutions Involved: Department of the Interior Southeast Climate Science Center at North Carolina State University, Department of Biology at Washington University in St. Louis, Centre for Ecological and Evolutionary Studies at the University of Groningen, Centre for Biodiversity Dynamics at Norwegian University of Science and Technology, Department of Ecology, Evolution and Environmental Biology at Columbia University.

Summary:

Variability is becoming more frequent and unpredictable in today’s environment. As a result of this variation in environmental conditions, there is a pressing need for species to cope with and adapt to this phenomenon. Understanding how organisms adapt to changes in their environments is a pivotal idea in evolution and ecology. Evolutionary responses to ecological parameters, such as ambient temperatures or precipitation, can help determine species’ adaptation to environmental change. In a study conducted by Carlos A. Botero, Franz J. Weissing, Jonathan Wright, and Dustin R. Rubenstein, these issues are addressed and analyzed. They study the changes in the predictability of environmental variation that may ultimately affect population feasibility. These biologists develop a model that predicts evolutionary responses to fluctuating environmental conditions and explores the potential consequences of altered environmental cycles. The model indicates that there remains a possibility that fairly large environmental changes can lead to extinction. The model also shows that “parameter space determined by different combinations of predictability and timescale of environmental variation is partitioned into distinct regions where a single mode of response (reversible phenotypic plasticity, irreversible phenotypic plasticity, bet-hedging, or adaptive tracking) has a clear selective advantage over all others”. Furthermore, the model demonstrates that despite evolutionary accommodation, most changes in the environment involve transitions between regions. This, ultimately, can result in rapid population collapse and even extinction. Finally, the model shows that different genetic backgrounds can influence the probability of extinction during such transitions. These insights essentially portray the value of evolutionary thinking in the study of global environmental change. Intrinsically, through evolutionary simulations, these biologists show that adaptive responses consistently evolve under and heavily depend on the different timescales and predictabilities of environmental variation. “Specifically, the potential for adaption to changes in the predictability or timescale of environmental change appears to depend more on the location of parameter space that populations are moving into than on the magnitude of the change itself.” In conclusion, this study helps us expand our understanding of how populations and species may respond to environmental changes and challenges.

Citation:

Botero, C.A., F.J. Weissing, J. Wright, and D.R. Rubenstein. 2014. Evolutionary Tipping Points in the Capacity to Adapt to Environmental Change. Proceedings of the National Academy of Sciences 112:184-189.

Social interaction helps bats decide what to eat

Date Published: July 22, 2014

Source: Behavioral Ecology

Institutions involved: University of Konstanz; Department of Biology, Planck Institute for Ornithology; School of Human Evolution & Social Change; Arizona State University.

Summary: A study conducted by  M. Teague O’Mara, Dina K.N. Dechmann,  and Rachel A. Page  in the Behavioral Ecology journal proposes the possibility of social interaction having a great impact on what food a species of bats decide to eat.

                A study conducted by  M. Teague O’Mara, Dina K.N. Dechmann,  and Rachel A. Page  in the journal of Behavioral Ecology proposes the possibility of social cues having a great impact on what food a species of bats decide to eat. Published July 22, 2012, the journal goes into depth about the different social interactions observed among the Uroderma bilobatum species of bats. Furthermore, several conclusions are drawn about what happens when a bat returns to the roost having eaten a new or novel food.

                Researchers have long hypothesized, and now theorized, that animals have the ability to gather information from other animals that enter or pass by the roost. Although true, what is incredible is not that they have been found to have this ability, but that they can differentiate between reliable and unreliable sources in the form of cues. When individuals come into the roost, they exhibit a sort of signal, or cue, to its roostmates indicating that it had just eaten. These cues could potentially be a change in weight, increased grooming, or odor on breath or fur of the individual. A group of researchers found that these cues can affect the feeding choices of other individuals for a significant amount of time.

               The method involved novel flavored bananas, as the bats are used to a diet of banana. The Uroderma bilobatum were captured and recorded for their mass, forearm length, reproductive status, age, and sex. They were then tagged ad monitored daily for the purpose of their well-being. All of the participants came from the same roost to guarantee their familiarity with one another. The four experiments tested the reaction of bats to novel odor exposure, social information transfer in captivity and in nature, and the ability to discriminate information given by two demonstrators.

               The first experiment conducted by O'Mara and his team involved a dish of novel flavoring mixed with banana that was placed in a mesh enclosure, so that the individual bats could smell but not access it for the purpose of familiarization. The bats were then offered two dishes of food, one with the "familiar" smell and another novel flavored "unfamiliar" dish. In the second experiment, a few bats were taken out of their cage, fed a flavored sugar solution and returned to their cage to eat more bananas. The demonstrator bats were individually given a choice of either bananas with the same novel flavor or a new flavor. The third experiment began with the capture of several free range bats. They were held in a cage and fed a flavored banana-sugar water mixture then freed after two days. The group of researchers then captured members of the roosts they captured the demonstrator bats from and were offered bananas flavored with their demonstrator's flavor or another flavor. In the fourth experiment, O'Mara and his team fed two demonstrators, the first was fed novel-flavored bananas and the second was fed an unflavored sugar solution and then a novel-flavored banana juice mixture was applied to its fur.

                The team found that interaction with a novel food odor wasn't enough for a food bias to form. Furthermore, observer bats were more likely to consume food eaten by demonstrator bats earlier. The fundamental finding is that information gathered from cues was likely to remain in a roost for a few days afterward. This ties into what researchers already know; animals interact and provide one another with information about their environment to continue the struggle to survive.

CITATION:  O'Mara, M.T, D.K.N Dechmann, and R.A Page. 2014. Frugivorous bats evaluate the quality of social information when choosing novel foods. Behavioral Ecology 25(5): 1233–1239.