Chrysemys Research Articles

Is the hypoxic ventilatory response driven by blood oxygen concentration?

![Figure][1] Bill Milsom and Tobias Wang discuss the impact of Mogens Glass, Robert Boutilier and Norbert Heisler's classic paper ‘Ventilatory control of arterial P O2 in the turtle Chrysemys picta bellii : Effects of temperature and hypoxia’, published in Journal of Comparative

Transcriptomic responses to environmental temperature by turtles with temperature-dependent and genotypic sex determination assessed by RNAseq inform the genetic architecture of embryonic gonadal development.

Vertebrate sexual fate is decided primarily by the individual’s genotype (GSD), by the environmental temperature during development (TSD), or both. Turtles exhibit TSD and GSD, making them ideal to study the evolution of sex determination. Here we analyze temperature-specific gonadal transcriptomes (RNA-sequencing validated by qPCR) of painted turtles (Chrysemys picta TSD) before and during the thermosensitive period, and at equivalent stages in soft-shell turtles (Apalone spinifera—GSD), to test whether TSD’s and GSD’s transcriptional circuitry is identical but deployed differently between mechanisms. Our data show that most elements of the mammalian urogenital network are active during turtle gonadogenesis, but their transcription is generally more thermoresponsive in TSD than GSD, and concordant with their sex-specific function in mammals [e.g., upregulation of Amh, Ar, Esr1, Fog2, Gata4, Igf1r, Insr, and Lhx9 at male-producing temperature, and of β-catenin, Foxl2, Aromatase (Cyp19a1), Fst, Nf-kb, Crabp2 at female-producing temperature in Chrysemys]. Notably, antagonistic elements in gonadogenesis (e.g., β-catenin and Insr) were thermosensitive only in TSD early-embryos. Cirbp showed warm-temperature upregulation in both turtles disputing its purported key TSD role. Genes that may convert thermal inputs into sex-specific development (e.g., signaling and hormonal pathways, RNA-binding and heat-shock) were differentially regulated. Jak-Stat, Nf-κB, retinoic-acid, Wnt, and Mapk-signaling (not Akt and Ras-signaling) potentially mediate TSD thermosensitivity. Numerous species-specific ncRNAs (including Xist) were differentially-expressed, mostly upregulated at colder temperatures, as were unannotated loci that constitute novel TSD candidates. Cirbp showed warm-temperature upregulation in both turtles. Consistent transcription between turtles and alligator revealed putatively-critical reptilian TSD elements for male (Sf1, Amh, Amhr2) and female (Crabp2 and Hspb1) gonadogenesis. In conclusion, while preliminary, our data helps illuminate the regulation and evolution of vertebrate sex determination, and contribute genomic resources to guide further research into this fundamental biological process.

Characterization of melanin-concentrating hormone (MCH) and its receptor in chickens: Tissue expression, functional analysis, and fasting-induced up-regulation of hypothalamic MCH expression

Melanin-concentrating hormone (MCH) is a neuropeptide expressed in the brain and exerts its actions through interaction with the two known G protein-coupled receptors, namely melanin-concentrating hormone receptor 1 and 2 (MCHR1 and MCHR2) in mammals. However, the information regarding the expression and functionality of MCH and MCHR(s) remains largely unknown in birds. In this study, using RT-PCR and RACE PCR, we amplified and cloned a MCHR1-like receptor, which is named cMCHR4 according to its evolutionary origin, and a MCHR2 from chicken brain. The cloned cMCHR4 was predicted to encode a receptor of 367 amino acids, which shares high amino acid identities with MCHR4 of ducks (90%), western painted turtles (85%), and coelacanths (77%), and a comparatively low identity to human MCHR1 (58%) and MCHR2 (38%), whereas chicken MCHR2 encodes a putative C-terminally truncated receptor and is likely a pseudogene. Using cell-based luciferase reporter assays or Western blot, we further demonstrated that chicken (and duck) MCHR4 could be potently activated by chicken MCH1–19, and its activation can elevate calcium concentration and activate MAPK/ERK and cAMP/PKA signaling pathways, indicating an important role of MCHR4 in mediating MCH actions in birds. Quantitative real-time PCR revealed that both cMCH and cMCHR4 mRNA are expressed in various brain regions including the hypothalamus, and cMCH expression in the hypothalamus of 3-week-old chicks could be induced by 36-h fasting, indicating that cMCH expression is correlated with energy balance. Taken together, characterization of chicken MCH and MCHR4 will aid to uncover the conserved roles of MCH across vertebrates.

A test of an antipredatory function of conspicuous plastron coloration in hatchling turtles

Bright colorations in animals are sometimes an antipredatory signal meant to startle, warn, or deter a predator from consuming a prey organism. Freshwater turtle hatchlings of many species have bright ventral coloration with high internal contrast that may have an antipredator function. We used visual modeling and field experiments to test whether the plastron coloration of Chrysemys picta hatchlings deters predators. We found that bird predators can easily distinguish hatchling turtles from their backgrounds and can easily see color contrast within the plastron. Raccoons cannot easily discriminate within-plastron color contrast but can see hatchlings against common backgrounds. Despite this, we found that brightly-colored, high contrast, replica turtles were not attacked less than low contrast replica turtles, suggesting that the bright coloration is not likely to serve an antipredatory function in this context. We discuss the apparent lack of innate avoidance of orange coloration in freshwater turtles by predators and suggest that preference and avoidance of colors are context-dependent. Since the bright colors are likely not a signal, we hypothesize that the colors may be caused by pigments deposited in tissue from maternal reserves during development. In most species, these pigments fade ontogenetically but they may have important physiological functions in species that maintain the bright coloration throughout adulthood.

Effects of low-oxygen conditions on embryo growth in the painted turtle, Chrysemys picta.

Low-oxygen conditions (hypoxia; <21% O2 ) are considered unfavorable for growth; yet, embryos of many vertebrate taxa develop successfully in hypoxic subterranean environments. Although enhanced tolerance to hypoxia has been demonstrated in adult reptiles, such as in the painted turtle (Chrysemys picta), its effects on sensitive embryo life stages warrant attention. We tested the hypothesis that short-term hypoxia negatively affects growth during day 40 of development in C. picta, when O2 demands are highest in embryos. A brief, but severe, hypoxic event (5% O2 for 0.5 h) moderately affected embryo growth, causing a 13% reduction in mass (relative to a normoxic control). The same condition had no effect during day 27; instead, a nearly anoxic event (1% O2 for 72 h) caused a 5% mass reduction. All embryos survived the egg incubation period. Our study supports the assumption that reptilian embryos are resilient to intermittently low O2 in subterranean nests. Further work is needed to ascertain responses to suboptimal O2 levels while undergoing dynamic changes in developmental physiology.

Transcriptomic alterations in the brain of painted turtles (Chrysemys picta) developmentally exposed to bisphenol A or ethinyl estradiol.

Developmental exposure of turtles and other reptiles to endocrine-disrupting chemicals (EDCs), including bisphenol A (BPA) and ethinyl estradiol (EE), can stimulate partial to full gonadal sex-reversal in males. We have also recently shown that in ovo exposure to either EDC can induce similar sex-dependent behavioral changes typified by improved spatial learning and memory or possibly feminized brain responses. Observed behavioral changes are presumed to be due to BPA- and EE-induced brain transcriptomic alterations during development. To test this hypothesis, we treated painted turtles (Chrysemys picta) at developmental stage 17, incubated at 26°C (male-inducing temperature), with 1) BPA (1 ng/µl), 2) EE (4 ng/µl), or 3) vehicle ethanol (control group). Ten months after hatching and completion of the behavioral tests, juvenile turtles were euthanized, brains were collected and frozen in liquid nitrogen, and RNA was isolated for RNA-Seq analysis. Turtles exposed to BPA clustered separately from EE-exposed and control individuals. More transcripts and gene pathways were altered in BPA vs. EE individuals. The one transcript upregulated in both BPA- and EE-exposed individuals was the mitochondrial-associated gene, ND5, which is involved in oxidative phosphorylation. Early exposure of turtles to BPA increases transcripts linked with ribosomal and mitochondrial functions, especially bioenergetics, which has been previously linked with improved cognitive performance. In summary, even though both BPA and EE resulted in similar behavioral alterations, they diverge in the pattern of neural transcript alterations with early BPA significantly upregulating several genes involved in oxidative phosphorylation, mitochondrial activity, and ribosomal function, which could enhance cognitive performance.

Morbidity and mortality in reptiles presented to a wildlife care facility in Central Illinois

We examined morbidity and mortality of 200 reptiles, representing 13 different species that were presented to the University of Illinois Wildlife Medical Clinic (WMC) from 2003 to 2010. Snapping turtles (Chelydra serpentine; n = 46), box turtles (Terrapene sp.; n = 43), painted turtles (Chrysemys picta; n = 37), and red-eared slider turtles (Trachemys scripta elegans; n = 33) were the most frequently seen species. Turtles were significantly more likely to be presented to the WMC following collision with a motor vehicle (n = 73) than any other reason, including idiopathic trauma (i.e., trauma of unknown origin; n = 25) or infectious disease (n =18). The findings from this cross-sectional study suggest a potential for community education in limiting reptile traumas resulting in presentations to a wildlife hospital.

Genetic effects of landscape, habitat preference and demography on three co-occurring turtle species.

Expanding the scope of landscape genetics beyond the level of single species can help to reveal how species traits influence responses to environmental change. Multispecies studies are particularly valuable in highly threatened taxa, such as turtles, in which the impacts of anthropogenic change are strongly influenced by interspecific differences in life history strategies, habitat preferences and mobility. We sampled approximately 1500 individuals of three co-occurring turtle species across a gradient of habitat change (including varying loss of wetlands and agricultural conversion of upland habitats) in the Midwestern USA. We used genetic clustering and multiple regression methods to identify associations between genetic structure and permanent landscape features, past landscape composition and landscape change in each species. Two aquatic generalists (the painted turtle, Chrysemys picta, and the snapping turtle Chelydra serpentina) both exhibited population genetic structure consistent with isolation by distance, modulated by aquatic landscape features. Genetic divergence for the more terrestrial Blanding's turtle (Emydoidea blandingii), on the other hand, was not strongly associated with geographic distance or aquatic features, and Bayesian clustering analysis indicated that many Emydoidea populations were genetically isolated. Despite long generation times, all three species exhibited associations between genetic structure and postsettlement habitat change, indicating that long generation times may not be sufficient to delay genetic drift resulting from recent habitat fragmentation. The concordances in genetic structure observed between aquatic species, as well as isolation in the endangered, long-lived Emydoidea, reinforce the need to consider both landscape composition and demographic factors in assessing differential responses to habitat change in co-occurring species.

Phenotypic plasticity of nest timing in a post-glacial landscape: how do reptiles adapt to seasonal time constraints?

Life histories evolve in response to constraints on the time available for growth and development. Nesting date and its plasticity in response to spring temperature may therefore be important components of fitness in oviparous ectotherms near their northern range limit, as reproducing early provides more time for embryos to complete development before winter. We used data collected over several decades to compare air temperature and nest date plasticity in populations of painted turtles and snapping turtles from a relatively warm environment (southeastern Michigan) near the southern extent of the last glacial maximum to a relatively cool environment (central Ontario) near the northern extent of post-glacial recolonization. For painted turtles, population-level differences in reaction norm elevation for two phenological traits were consistent with adaptation to time constraints, but no differences in reaction norm slopes were observed. For snapping turtle populations, the difference in reaction norm elevation for a single phenological trait was in the opposite direction of what was expected under adaptation to time constraints, and no difference in reaction norm slope was observed. Finally, among-individual variation in individual plasticity for nesting date was detected only in the northern population of snapping turtles, suggesting that reaction norms are less canalized in this northern population. Overall, we observed evidence of phenological adaptation, and possibly maladaptation, to time constraints in long-lived reptiles. Where present, (mal)adaptation occurred by virtue of differences in reaction norm elevation, not reaction norm slope. Glacial history, generation time, and genetic constraint may all play an important role in the evolution of phenological timing and its plasticity in long-lived reptiles.

Is righting response lateralized in two species of freshwater turtles?

Laterality has been found in a variety of reptiles. In turtles, one important behaviour is the righting response. Here, we studied laterality of righting response of two species of freshwater turtles, the Painted Turtle (Chrysemys picta) and the Eastern Musk Turtle (Sternotherus odoratus). We found evidence of individual-level laterality in righting response inC. picta, but notS. odoratus. Neither species showed evidence of population-level laterality in righting response. Our results suggest that there is variation in the extent of laterality of righting response in turtles. Possible explanations for variation in laterality of righting response in turtles include shell shape and use of terrestrial habitats. However, more species of turtles need to be examined to demonstrate any general patterns in laterality of righting response in turtles.

The effects of pH and Pi on tension and Ca2+ sensitivity of ventricular myofilaments from the anoxia-tolerant painted turtle

We aimed to determine how increases in intracellular H+ and inorganic phosphate (Pi) to levels observed during anoxic submergence affect contractility in ventricular muscle of the anoxia-tolerant Western painted turtle, Chrysemys picta bellii Skinned multicellular preparations were exposed to six treatments with physiologically relevant levels of pH (7.4, 7.0, 6.6) and Pi (3 and 8 mmol l-1). Each preparation was tested in a range of calcium concentrations (pCa 9.0-4.5) to determine the pCa-tension relationship for each treatment. Acidosis significantly decreased contractility by decreasing Ca2+ sensitivity (pCa50) and tension development (P<0.001). Increasing [Pi] also decreased contractility by decreasing tension development at every pH level (P<0.001) but, alone, did not affect Ca2+ sensitivity (P=0.689). Simultaneous increases in [H+] and [Pi] interacted to attenuate the decreased tension development and Ca2+ sensitivity (P<0.001), possibly reflecting a decreased sensitivity to Pi when it is present as the dihydrogen phosphate form, which increases as pH decreases. Compared with that of mammals, the ventricle of turtles exhibits higher Ca2+ sensitivity, which is consistent with previous studies of ectothermic vertebrates.

Condition and mortality of western painted turtle collected as bycatch in modified fyke nets during fish population assessments

ABSTRACTInformation concerning turtle bycatch and its possible ramifications during biological sampling in freshwater systems is limited. Having such information will enable fisheries researchers and managers to modify fish sampling procedures to potentially minimize any impacts on turtle populations. Therefore, our objective was to utilize reflex response to characterize stress and mortality of western painted turtles (Chrysemys picta bellii) captured as bycatch in modified fyke nets during fish population assessments. Reflex-response-based condition classification (i.e. good, poor, unresponsive) data were collected from May to September during fish population assessments in 38 lakes and seven impoundments in northeast South Dakota from 2012 to 2014. We evaluated the relationship between observed condition and water temperature during two time periods, by turtle gender and size. Turtle bycatch mortality was assessed from June to September during fish population assessments in 14 lakes and three impoundments during 2013 and 2014. Delayed (i.e. overnight) mortality was determined for poor and unresponsive condition classifications and the relationship between observed mortality and water temperature for two time periods, by turtle gender and size was evaluated. Turtle condition decreased as water temperature increased. Condition was poorer during the May and June time period than August and September. Female turtles were in significantly worse condition than males. Condition was not related to turtle size. We observed varying mortality rates across condition classifications and the total estimated delayed mortality rate of known sex turtles was 36.4%. Mortality increased as temperature increased. Delayed mortality rates varied between the two sampling periods with higher mortality rates during the May and June time period. Female turtles had higher mortality rates than males. Delayed mortality did not vary by turtle size. Understanding the negative effects on bycatch during biological sampling is important to provide justification for the development and implementation of measures to protect non-target species.

Difference in exposure of water birds to covered and uncovered float muskrat sets

Muskrats Ondatra zibethicus are a popular furbearer species across much of North America. Float sets have gained popularity due to the ease of use and effectiveness of capturing muskrats. Little to no research has been conducted on muskrat float sets, especially on the impacts the float sets have on non‐target animals. In North Dakota, USA, regulations allowed trappers to use float sets during the spring season, but float sets were required to have a covering made of wire mesh, wood or plastic and no opening larger than 20.32 cm (8 inches) in an effort to minimize the incidental take of non‐target species. We aimed to determine if there was any non‐target capture injury or mortality risk on float muskrat sets. We conducted a study to compare rates of incidental take in covered (2.54×2.54 cm and 15.24×15.24 cm wire mesh) and uncovered float sets. We trapped muskrats in fall (1191 trap nights) and spring (3054 trap nights) from 2012–2014 at four study areas in North Dakota. Over four trapping periods (two fall and two spring seasons), 490 muskrats and seven non‐target species were captured. Non‐target species included three black‐crowned night heron Nycticorax nycticorax, two blue‐winged teal Anas discors and two painted turtles Chrysemys picta. All avian non‐target species were captured on uncovered floats. Camera trap data showed that ducks were 10.1 times less likely to be on floats than other types of water birds (e.g. herons). Covers did not negatively influence muskrat captures, but smaller mesh sizes appeared to deter birds from climbing on top of floats. All but one avian non‐target capture occurred after 1 May (closing of North Dakota's spring muskrat trapping season) each year, suggesting that season dates may be an important factor to consider in attempts to reduce incidental take of protected bird species.

Biologgers reveal post-release behavioural impairments of freshwater turtles following interactions with fishing nets

Bycatch, the incidental capture of non-target organisms, occurs in most commercial fisheries. Although immediate bycatch mortality is frequently documented in fisheries, detrimental sub-lethal effects and potential post-release mortality remain largely unknown despite the potential population-level consequences. Turtles are captured as bycatch and their populations are vulnerable to slight increases in adult mortality. In eastern Ontario, turtles are frequently captured as bycatch in a small-scale freshwater commercial fyke-net fishery and, currently, the fate of discarded turtles is unknown. We wished to determine the effect of fyke-net capture on post-release survival and behaviour in eastern musk turtles Sternotherus odoratus and painted turtles Chrysemys picta. We used biologgers equipped with tri-axial acceleration, depth and temperature sensors to document locomotor activity, vertical distribution, and temperature use of entrapped (exposed to forced submergence for 4 h) and control turtles upon release. Overall dynamic body acceleration was used as a measure of post-release activity for the first hour, first 6 h, and first 48 h. Post-release mortality was not detected. Turtles subjected to entrapment exhibited lower activity during the first 6 h following release, and their vertical distribution and temperature use differed in the first 2 h following release, but these effects disappeared after 48 h, suggesting turtles have the ability to recover. Quantifying the post-release mortality and sub-lethal effects of entrapment is important for estimating the population effects associated with bycatch.

Olfaction as a Cue for Nest-Site Choice in Turtles

Nest-site choice in turtles has a demonstrated impact on their fitness. Previous studies of nest-site choice have focused on environmental factors potentially affecting that choice (e.g., temperature, insolation, soil type, or moisture). Observations of nesting of painted turtles (Chrysemys picta) at the Crescent Lake National Wildlife Refuge in the Nebraska Sandhills suggest that females might use olfactory cues (specifically odors of other nesting females) to choose nest sites. We tested this hypothesis indirectly by using the nearest neighbor (nest) distance algorithm in ArcMap 10.1. Our results for nests in 2012–2014 were mixed, with nesting at some sites, in some years, and by some turtles occurring nonrandomly, in very close proximity to previous nests. Preliminary experimental data from 2015 using urine-treated sites in primary nesting areas also suggested that females showed more interest in those sites than sites moistened with equal amounts of water. These data provide some support for the use of nest odor as an important cue for nest-site choice in turtles, but they are insufficient to reject the possibility of the simultaneous use of other fine-scale environmental cues.

Flight Initiation Distance in a Freshwater Turtle,Chrysemys picta

Abstract Many wild animals are subjected to anthropogenic stressors in the form of direct human disturbances from recreational activities. However, for many species it is unknown how these stressors affect individual fitness and behavior. We tested whether painted turtles (Chrysemys picta), an imperiled freshwater species, would allow closer human approach as measured by the flight initiation distance in the regular presence of humans compared with turtles not exposed to humans. We collected data at a site closed to recreation and at one with regular recreation and found that painted turtles regularly exposed to the presence of humans had significantly shorter average flight initiation distances compared with those at the nonrecreation site. The ability of turtles to tolerate closer human approaches in recreational areas may allow turtle populations to coexist in the presence of some recreational uses.

Using Behavioral Observations to Develop Escape Devices for Freshwater Turtles Entrapped in Fishing Nets

AbstractThe drowning of freshwater turtles following incidental capture in fishing gear has the potential to cause population declines. Fyke nets can be equipped with bycatch reduction devices that enable the escape of turtles before they drown. We employed quantitative and qualitative behavioral observations (with action cameras deployed underwater) to develop a new, collapsible, escape bycatch-reduction device that mounts internally in the terminal end of a fyke net. We also used behavioral observations to identify areas of the net most used by turtles, thus revealing the most logical placement for an escape bycatch-reduction device. When turtles were introduced into modified nets, escape was rapid (mean of 12.4 min), with 100% escape for map Graptemys geographica and musk turtles Sternotherus odoratus and 94% escape for painted turtles Chrysemys picta. Our preliminary field trials indicated that modified fyke nets decreased the capture rate of turtles relative to unmodified nets. Escape devices can be used as a key component of a bycatch reduction program and be particularly effective when paired with exclusion bycatch-reduction devices. The escape device developed in this study can potentially be used in the local fishery or modified for other fisheries. The use of behavioral observation to guide the development of bycatch reduction devices may provide an extra tool for managers to increase selectivity and maintain sustainable harvests of target fish.

Using Pharmacological Manipulation and High-precision Radio Telemetry to Study the Spatial Cognition in Free-ranging Animals.

An animal's ability to perceive and learn about its environment plays a key role in many behavioral processes, including navigation, migration, dispersal and foraging. However, the understanding of the role of cognition in the development of navigation strategies and the mechanisms underlying these strategies is limited by the methodological difficulties involved in monitoring, manipulating the cognition of, and tracking wild animals. This study describes a protocol for addressing the role of cognition in navigation that combines pharmacological manipulation of behavior with high-precision radio telemetry. The approach uses scopolamine, a muscarinic acetylcholine receptor antagonist, to manipulate cognitive spatial abilities. Treated animals are then monitored with high frequency and high spatial resolution via remote triangulation. This protocol was applied within a population of Eastern painted turtles (Chrysemys picta) that has inhabited seasonally ephemeral water sources for ~100 years, moving between far-off sources using precise (± 3.5 m), complex (i.e., non-linear with high tortuosity that traverse multiple habitats), and predictable routes learned before 4 years of age. This study showed that the processes used by these turtles are consistent with spatial memory formation and recall. Together, these results are consistent with a role of spatial cognition in complex navigation and highlight the integration of ecological and pharmacological techniques in the study of cognition and navigation.

Aspects of the Reproductive Ecology of Female Turtles in New Mexico

Abstract. Data on reproductive ecology of turtles in New Mexico are limited, and some species living there are among the least studied in the United States. We trapped 4 native species of turtles (Apalone spinifera, Chrysemys picta, Pseudemys gorzugi, and Trachemys gaigeae gaigeae) in the Rio Grande and Black River (Pecos River drainage) of New Mexico in June 2012 and 2013 to collect data on female reproductive ecology, including clutch size, egg size, timing of egg production, and percentage of gravid females. During our sampling, we found shelled eggs via X-radiography in only 3 native species: C. picta, P. gorzugi, and T. g. gaigeae. Clutch and egg sizes were within the range of previously reported values, although clutch size for P. gorzugi (10 eggs) is only the second published record for that data-deficient species. Clutch size increased with body size in T. g. gaigeae. We observed few differences between reproductive parameters for turtles in New Mexico and their conspecifics and congeners elsewher...

Assessment of anoxia tolerance and photoperiod dependence of GABAergic polarity in the pond snail Lymnaea stagnalis

The pond snail Lymnaea stagnalis is reported to be anoxia-tolerant and if the tolerance mechanism is similar to that of the anoxia-tolerant painted turtle, GABA should play an important role. A potentially confounding factor investigating the role of GABA in anoxia tolerance are reports that GABA has both inhibitory and excitatory effects within L. stagnalis central ganglion. We therefore set out to determine if seasonality or photoperiod has an impact on: 1) the anoxia-tolerance of the intact pond snail, and 2) the response of isolated neuroganglia cluster F neurons to exogenous GABA application. L. stagnalis maintained on a natural summer light cycle were unable to survive any period of anoxic exposure, while those maintained on a natural winter light cycle survived a maximum of 4h. Using intracellular sharp electrode recordings from pedal ganglia cluster F neurons we show that there is a photoperiod dependent shift in the response to GABA. Snails exposed to a 16h:8h light:dark cycle in an environmental chamber (induced summer phenotype) exhibited hyperpolarizing inhibitory responses and those exposed to a 8h:16h light:dark cycle (induced winter phenotype) exhibited depolarizing excitatory responses to GABA application. Using gramicidin-perforated patch recordings we also found a photoperiod dependent shift in the reversal potential for GABA. We conclude that the opposing responses of L. stagnalis central neurons to GABA results from a shift in intracellular chloride concentration that is photoperiod dependent and is likely mediated through the relative efficacy of cation chloride co-transporters. Although the physiological ramifications of the photoperiod dependent shift are unknown this work potentially has important implications for the impact of artificial light pollution on animal health.