Category: All Posts Page 31 of 146

SICB 2020: Sex-biased Parasitism and the Expression of a Sexual Signal in a Tropical Forest Lizard

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On January 10, 2020

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Panamanian slender anole (Anolis apletophallus) (Photo Credit: Dr. Christian Cox)

Male sexual signals, and their often-associated distinct phenotypic and behavioral displays, have been hypothesized to have evolved from multiple sources. Two of which include the Good Genes hypothesis, which suggests sexual signals serve as an honest signal to potential mates, and the Immunocompetence Handicap hypothesis, which indicates trade-offs to elaborate signals. However, Dr. Christian Cox, an assistant professor in the Biology Department at Florida International University, thinks of these as a continuum rather than opposing hypotheses. The vibrant dewlaps of Anolis species serve as an excellent model system to address questions related to this continuum. Dr. Cox’s lab has documented sex-biased parasitism, which he discussed on Monday at SICB 2020. 

Dr. Christian Cox

The Panamanian slender anole (Anolis apletophallus) is known to host ectoparasitic trombiculid mites (also known as chigger mites). In this species, males and females are roughly the same size and, as with most anole species, males carry a large, colorful dewlap beneath their chins. Dr. Cox asked whether males and females of this species differ in the attachment site and intensity of mite infestations and whether any other factors (e.g., energetics) might influence infection. Using a combination of field and laboratory studies, Dr. Cox and his colleagues quantified the number of mites, prevalence, and intensity of infestation on individuals. He also measured mass, snout-vent length, and dewlap size. Following this, he collected fat bodies, livers, and gonads to investigate differences in energetics. 

Dr. Cox found that males were more likely to have mites on their dewlap whereas females had more mites in the inguinal and axillary regions. Additionally, large males had more mites than smaller ones and there was a significant correlation between the size of the dewlap and the number of mites. Dr. Cox also found that there was a negative relationship between fat body mass and the total number of mites. In other words, males with a heavier fat body had less mites. In females, there was a positive relationship between gonad size and the number of mites. These findings suggest sex-dependent factors influence ectoparasite load and are indicative of trade-offs to male sexual signals. 

SICB 2020: Arginine Vasotocin Stimulates Chemical Communication and Social Behavior in Anolis carolinensis

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On January 10, 2020

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Dr. Stephanie Campos presenting her research at SICB 2020

A captive green anole (Anolis carolinensis) (Photo Credit: Dr. Stephanie Campos)

Exocrine signals (e.g., pheromones) and endocrine signals, like those associated with chemosensory organs, stimulate communication among and within species. Dr. Stephanie Campos is especially interested in the endocrine signals of reptiles and highlighted some of her work at SICB 2020. 

Dr. Campos is a postdoctoral research fellow at Georgia State University Center for Behavioral Neuroscience and Neuroscience Institute in Dr. Walt Wilczynski’s lab. She investigated the role of arginine vasotocin (AVT), a modulator of social interaction similar to the mammalian homologue vasopressin, on reptilian chemosensory systems. Previous work in green anoles (Anolis carolinensis) showed that AVT reduces aggressive visual display rates and stimulates females to display more than untreated counterparts.

In this study, Dr. Campos and colleagues tested the role of chemosensory systems in A. carolinensis by injecting resident males with AVT and introducing a male or female intruder. Ten minutes after injecting with AVT or a control solution, an untreated male or female was placed in the tank for thirty minutes. Chemical behavior, including tongue flick, jaw/chin rub, lip smack, lick, fecal/urine deposit, or cloacal rub were recorded.

They found that male intruders displayed more of these chemical behaviors toward individuals treated with AVT than controls. Additionally, males treated with AVT displayed quicker (e.g., tongue-flicking) to female intruders than controls. Dr. Campos speculates that AVT might boost production of odor cues or interior mediated endocrine-mechanisms. This might serve as an indication for multimodal communication in reptiles.

You can learn more about Dr. Campos’ research by following her on Twitter. 

SICB 2020: Acute Interactions between Green and Brown Anoles

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On January 9, 2020

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Jordan Bush giving her talk on the interaction between green and brown anoles at SICB 2020

Green and brown anole interacting within Jordan’s enclosures.

As brown anoles (Anolis sagrei) become more and more abundant, many people (trained and citizen scientists alike) are intrigued with exactly how the native green anole (A. carolinensis) will respond. Newspaper articles still report on these interspecific interactions, and some recent research has shown the brown anoles can be quite mean to the native green. Thankfully, it seems that the green anole may simply be moving higher into the canopy and aren’t being merely driven to extinction by the invading brown. However, we do not yet understand the nuances of how green anoles respond when brown anoles first arrive to a new location, and that’s where Jordan Bush, a sixth year PhD student in Dan Simberloff’s lab at the University of Tennessee, Knoxville, comes in.

To understand how green anoles immediately react to the novel presence of brown anoles, Jordan built 5 x 5 x 5m enclosures in which she placed 6 female and 6 male green anoles. These animals then set up territories and became acclimated to their new living space. Jordan quantified baseline behavior and territory sizes (in 3D!!!) for each individual in an enclosure.

Example 3D territories

After 10 days, Jordan introduced brown anoles in these enclosures, either two females and two males or four females and four males to investigate the effects of density, and quantified behavioral and territorial changes in the green anole. Being the careful researcher that she is, she also introduced the same number of green anoles to other enclosures so that she could show that any changes in behavior were not simply due to more animals being present. After 10 days of interacting with the brown anole, Jordan found no change in activity level, home range volume, or perch height, suggesting that, at least within an acute time frame, the green anole can handle its own against the brown anole.

SICB 2020: Impacts of a Novel Environment on a Tropical Anole Species

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On January 9, 2020

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Dan Nicholson at SICB 2020

Evolution has long thought to be a slow process, taking thousands if not millions of years. Recently, there has been a paradigm shift in how scientists think about evolution. We now know that we can observe evolution on a contemporary timescale, observable to the human eye. Dan Nicholson, a Ph.D. Candidate at Queen Mary University of London in Rob Knell’s lab, is working with Mike Logan and others to observe the effects of habitat change on the evolutionary ecology of Anolis apletophallus.

Dan and his team transplanted anoles from the mainland of Panama to several islands around Barro Colorado Island in July of 2017. Before release, they recorded the anoles’ morphological characteristics, including hindlimb and forelimb length, toe pad size, and head depth, and well as characteristics of their perch location, including height and width. Tracking changes in these characteristics can detect natural selection at work. At SICB 2019, Dan reported the results of the first generation of island anoles.

At SICB 2020, Dan included the trends of the second generation of island anoles. The preliminary results indicate the island anoles have continued to use wider perches than the mainland anoles. However, the majority of the island anole morphological traits now align with the mainland anoles. The exception is that hindlimb length of the island anoles decreased, while the mainland anoles hindlimb length has increased.

Some potential causes of these results, Dan speculates, include genetic drift due to the small population size. The islands started with a robust number of anoles, but over the two years of this study, their numbers have rapidly dwindled. Another possibility is the island anoles are aligning with the mainland anoles morphologically due to gene flow. In the future, Dan wants to further analyze the preliminary results from a population angle, looking at changes in groups of traits instead of individual traits.

You can learn more about Dan’s research by following him on twitter.

SICB 2020: Why Do Anole Heads Fail to Develop Properly When It’s Hot?

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On January 9, 2020

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Sylvia presenting her work at SICB 2020

Another SICB, another great presentation from Sylvia Nunez from Thom Sanger’s lab investigating how the interaction between heat and oxygen availability affects development in the brown anole (Anolis sagrei). Last year, Sylvia presented a poster showing that above 33°C, embryonic survival was greatly reduced and many embryos developed craniofacial malformations. With some potential nesting sites for anoles now exceeding 40°C, understanding mechanisms leading to decreased survival is critical.

Low oxygen at sublethal temperatures can recapitulate negative effects on craniofacial development at high temperatures.

As a follow up to this study, Sylvia set out to understand exactly how it is that heat and oxygen can interact to lead to craniofacial deformities. She posited several hypotheses and was able to eloquently test each one, including the neural degeneration hypothesis and the oxygen limitation hypothesis. Specifically, Sylvia noted that disruption in sonic hedgehog has been linked to facial development and that oxygen demand can often exceed oxygen supply at high temperatures.

First, Sylvia tested the oxygen limitation hypothesis by examining whether low oxygen coupled with sublethal (elevated) temperature conditions recapitulate the effects of craniofacial malformation under thermal stress. Previous work in the lab induced craniofacial malformation at 36°C; Sylvia showed you could mimic this effect using 33°C with low oxygen, with a greater rate of malformation than in 27°C (the standard control temperature) with atmospheric oxygen, 27°C with low oxygen, or 33°C with atmospheric oxygen. She then tested whether an increase in oxygen can rescue embryonic survival at high temperatures. To do so, she split eggs among two treatment conditions: 27°C with high oxygen and a hot nest site temperature with high oxygen. She found further support for the oxygen limitation hypothesis – when oxygen availability was increased above atmospheric conditions there were no differences in embryonic survival. Wow! Further, there were no craniofacial malformations in the high temperature treatment when oxygen conditions were high.

To follow up on this finding, she examined if oxidative stress could be the link between temperature and craniofacial malformations using superoxide dismutase (SOD), an enzyme that helps turn the superoxide radical (O2–) into oxygen (O2) or hydrogen peroxide (H2O2), as a marker for oxidative stress in the telencephalon. Indeed, within mere minutes of a temperature increase, SOD becomes upregulated, suggesting that thermal stress contributes to oxidative stress. But Sylvia didn’t stop there. She then treated some embryos with an SOD inhibitor to show that when SOD is absent craniofacial malformations appear.

Overall, Sylvia has very eloquently shown that increased temperature leads to craniofacial malformations via thermal effects on oxidative stress. I cannot wait to see what she presents next year!

SICB 2020: How Does Triiodothyronine Affect Lizard Metabolism?

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On January 9, 2020

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Undergraduate Yasmeen Khawaja with her poster at SICB 2020 in Austin, TX.

As with every year, Jerry Husak sent another crew of talented undergraduates to present great work at SICB 2020! This year, Yasmeen Khawaja presented a poster on her work on the role of triiodothyronine (T3) on lizard metabolism, with specific interests in its role on mitochondrial function and oxidative phosphorylation.

Yasmeen noted her interest in T3, stating that our understanding of thyroid hormones generally, and T3 specifically, has been a mixed bag of results in nonmammalian systems. To help remedy this, she injected male green anoles (Anolis carolinensis) with either 0.01 mg/g body weight of T3 (n = 20) or saline (n = 19) subcutaneously for 19 consecutive days. Interestingly, there were no apparent effects on change in animal mass nor their standard metabolic or mitochondrial respiration rates between the two treatment groups!

Overall, Yasmeen concluded that T3 may not be the biologically active form of thyroid hormone in ectotherms and plans to conduct tests with T4 in the future. I hope she presents those data at SICB 2021!

SICB 2020: Artificial Light at Night Suppresses CORT Rhythmicity

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On January 9, 2020

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Margaret McGrath at SICB 2020

If you look at a map of the United States at night, the urban areas are aglow with light pollution. Urban light pollution disrupts biological processes from gene expression to ecosystem composition across multiple taxa, including birds, insects, mammals, and fishes. With ever-increasing urbanization, understanding the effects of artificial light at night (ALAN) on organisms is crucial to future conservation efforts.

Margaret McGrath, an undergraduate in Dr. Christopher Howey’s lab at the University of Scranton, is examining the impact of ALAN on glucocorticoids in green anoles (Anoles carolinensis), which are commonly found in urban environments. Margaret specifically examined the impact of ALAN on the daily rhythmicity of corticosterone (CORT) and CORT responsiveness to an environmental stressor. She exposed green anoles to either a natural light-day cycle of 12 hours of light and 12 hours of dark or 24 hours of light. After six weeks of exposure, Margaret performed competitive immunoassays to measure baseline CORT levels at midnight and noon. Additionally, she measured CORT responsiveness after placing the green anoles in a bag for 30 minutes to simulate an environmental stressor.

Anoles not exposed to ALAN displayed an expected CORT daily rhythmicity with higher levels of CORT during the day than at night. Anoles exposed to ALAN lost this CORT rhythmicity and maintained CORT at a level intermediate to the other group. In contrast, ALAN does not appear to impact the anoles’ CORT responsiveness to environmental stressors. Her results suggest that green anoles exposed to ALAN are still able to respond to environmental stressors. However, there could be downstream effects from the loss of CORT rhythmicity because it has been linked to arrhythmic activity in mammalian studies.

In the future, Margaret plans to investigate if the natural CORT rhythmicity can be regained by anoles exposed to ALAN when placed back into a natural light-dark cycle. This future research can aid in determining the longevity of ALAN’s impacts on organisms. You can reach Margaret at margaret.mcgrath@scranton.edu and find more about her research on chowey.net, Dr. Howey’s website.

SICB 2020: Collecting Ecological Data from iNaturalist Observations: an Example with Anolis Lizards

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On January 9, 2020

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Chris Thawley presenting his work at SICB 2020

Citizen science is a collaboration between scientists and the general public to advance scientific research. A major citizen science project is iNaturalist. In iNaturalist, anyone can submit an observation of an organism, which includes the date and location. It provides a database over a large area and a long time that would be extremely costly for scientists alone to collect. However, the data’s suitability for ecological analysis is uncertain.

To shine some light on the robustness of citizen science data, Chris Thawley, a visiting assistant professor at Davidson College, worked in collaboration with Amy Kostka, an undergraduate at the University of Rhode Island. When the project was developed, Chris was a postdoc in Jason Kolbe’s lab at the University of Rhode Island. As Amy was unable to go into the field, iNaturalist provided the perfect opportunity for her to experience the research process. They decided to compare established hypotheses of native green anoles (Anolis carolinensis) and invasive brown anoles (Anolis sagrei) against the iNaturalist data. They first coded the anoles’ sex, habitat use, behavior, and morphology, and then compared their coded data against existing hypotheses.

Overall, they found that the iNaturalist data corresponded with existing hypotheses of green and brown anoles. Male brown anoles displayed more frequently than male green anoles, in accordance with results in this paper. Males had broken tails more frequently than females regardless of species, likely due to the more risky behaviors conducted by male anoles than females anoles. Green anoles perched more frequently on natural substrates and perched more frequently in a vertical orientation than brown anoles, in accordance with findings by Stuart et al. (2014). Additionally, the brown and green anoles’ reproductive time period (as measured by when hatchlings emerged) matched with the literature.

iNaturalist is a fantastic tool for individuals who are unable to conduct fieldwork, but still want the research experience. However, Chris pointed out that iNaturalist has spatial biases towards urban areas and temporal biases towards the present day. Additionally, it is necessary to sort and clean the data and to train individuals to standardize coding. This study demonstrates that iNaturalist is still a powerful tool and can be used to estimate phenological patterns, differences between sexes, and corroborate existing hypotheses. Chris hopes that, in the future, iNaturalist could be used to generate new hypotheses.

SICB 2020: Artificial Light Keeps Green Anoles Hungry!

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On January 8, 2020

In All Posts, New Research

There are so many great anole talks at SICB 2020, I’d be remiss if I didn’t take this opportunity to shed some light on some of our fantastic undergraduate researchers, who turned out in force to Austin this year! As I’m sure Dr. Kristin Winchell will tell you, anole lizards make awesome model organisms for studying the effects of city life and urbanization on wildlife.

Cities can be dangerous though. A lot of different urban environments will present wildlife that have not lived in cities with numerous pressures they might not have faced before, such as different surfaces and substrates on which to run, different temperatures, and even new predators. One of the relatively new pressures that goes along with city life is light at night, and artificial light to boot. If you’ve ever been too disturbed by light during the moonlight hours to sleep and rest, imagine how small lizards feel!

To address the effects of this pressure on green anoles (Anolis carolinensis), Michelle D’Alessandro, an undergraduate student at the University of Scranton working in the lab of Dr. Chris Howey, measured the effects of artificial light at night (I’m just going to call it ALAN) They exposed anoles to ALAN and described the effects of artificial light on metabolism in green anoles. Initially, they did not find any differences between metabolic rates when lizards were exposed to ALAN, however after a sufficient time period, anoles exposed to ALAN increased their metabolic rates during the evening, but not during the day! During this experiment, they also found that ALAN anoles were far hungrier and ate more often than lizards that weren’t exposed to light at night. The term ‘midnight snack’ definitely comes to mind here! Michelle suggests that much like when humans get exposed to changes in sleeping patterns, anoles undergo some energetic changes, causing them to eat more and having to burn more energy. Maybe next time think twice about keeping that porch light on during the waning hours of the evening- give the wildlife some much needed rest.

SICB 2020: Variation in Anole Sperm and Testis Morphology

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On January 8, 2020

In All Posts, New Research

Another star undergrad alert! If you’ve ever followed the work that comes out of Dr. Michele Johnson’s lab at Trinity University, you’ll know that she produces some incredible science and some even-more incredible undergraduate researchers. Isabela Carson is no exception!

Isabela’s poster was focused on studying intraspecific variation in lizard sperm and testis morphology- she described differences in the size and shape of different testis and sperm features for 6 different species of anole. A lot of this work was founded on Dr. Ariel Kahrl’s dissertation work on describing sperm evolution in anole lizards, and her collaborations with Dr. Johnson’s lab and students always produce some awesome talks and posters wherever they are presented. Isabela wanted to know if longer sperm are produced from lizard species that have larger seminiferous tubules- the part of the testis where sperm are produced, matured, and transported. She found an inconsistent pattern across anole lizards where larger tubules don’t always produce longer sperm.

In talking with Isabela, she noted that there are some big inconsistencies between the external morphology of testes and the sperm they produce, and that there might be some larger ecological or evolutionary patterns at work that go into describing how sperm evolve in different species. I would bet that one day we are going to have data on testis shape and size and sperm length for all anolis species, and there are going to be some awesome patterns and studies that come out of that work. And we definitely have to give heaps of credit to the awesome biologists who are working towards it!

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