Grégory Bulté

Estimating diet in individual pumpkinseed sunfish Lepomis gibbosus using stomach contents, stable isotopes and parasites

The diets of 99 pumpkinseed sunfish Lepomis gibbosus from a pair of small, adjacent lakes in Ontario, Canada, were estimated from their stomach contents, trophically transmitted parasites and stable isotopes of carbon and nitrogen in fish tissue. The three methods provided virtually unrelated information. There was no significant correlation in the importance of any prey item across all three methods. Fish with similar diets according to one method of estimating diet showed no tendency to be similar according to other methods. Although there was limited variation in fish size and the spatial scale of the study was small, both fish size and spatial origin showed comparatively strong associations with diet data obtained with all three methods. These results suggest that a multidisciplinary approach that accounts for fish size and spatial origins is necessary to accurately characterize diets of individual fish.

Implications of extreme sexual size dimorphism for thermoregulation in a freshwater turtle

Sexual size dimorphism (SSD) is a common phenomenon in animals. In many species females are substantially larger than males. Because body size plays a central role in modulating the body temperature (Tb) of ectotherms, intersexual differences in body size may lead to important intersexual differences in thermoregulation. In addition, because SSD is realized by differences in growth rate and because growth rate is strongly temperature dependent in ectotherms, a conflict between male reproductive behaviour and thermoregulation may affect the expression of SSD. In this study, we investigated the thermal implications of SSD in a reptile exhibiting spectacular female-biased SSD: the northern map turtle (Graptemys geographica). Over three seasons, we collected >150,000 measurements of Tb in free-ranging adult and juvenile northern map turtles using surgically implanted miniature temperature loggers. Northern map turtles exhibited seasonal patterns of thermoregulation typical of reptiles in northern latitudes, but we found that large adult females experienced a lower daily maximum Tb and a narrower daily range of Tb than adult males and small juvenile females. In addition, despite more time spent basking, large adult females were not able to thermoregulate as accurately as small turtles. Our findings strongly suggest that body size limits the ability to thermoregulate accurately in large females. By comparing thermoregulatory patterns between adult males and juvenile females of similar body size, we found no evidence that male reproductive behaviours are an impediment to thermoregulation. We also quantified the thermal significance of basking behaviour. We found, contrary to previous findings, that aerial basking allows northern map turtles to raise their Tb substantially above water temperature, indicating that basking behaviour likely plays an important role in thermoregulation.

Spatial Ecology of Northern Map Turtles (Graptemys geographica) in a Lotic and a Lentic Habitat

Abstract Lentic (i.e., lake) and lotic (i.e., river) environments differ in several biotic and abiotic variables such as water velocity, productivity, thermal regimes, and depth. These variables can interact with important factors such as sex, body size, and life-history stage to shape the spatial ecology of aquatic animals such as freshwater turtles. We used radio-telemetry to study seasonal movement patterns and home-range size of juvenile and adult Northern Map Turtles (Graptemys geographica) both in a small lake and in a large river in eastern Ontario, Canada. Adult females in the lotic environment moved longer distances and had larger home ranges than conspecifics from the lentic environment. Males and juvenile females at each site had similar patterns of space use. A seasonal effect on movement was only apparent for adult females in the lotic environment in which adult females moved longer distances during the nesting season. Differences in swimming abilities resulting from a larger body size, in natal homing, or in nest site availability are potential factors explaining the site difference in the spatial ecology of adult females. Our findings illustrate the complexity of interactions shaping patterns of space use by aquatic reptiles.

Estimating the Energetic Significance of Basking Behaviour in a Temperate-Zone Turtle

Abstract: Basking is a common thermoregulatory behaviour in many ectotherms, including reptiles. Because the key physiological processes affecting net energy retention (NER) are temperature dependent, ectotherms have the potential to modulate their energy budget by using basking behaviour. Many aquatic chelonians bask extensively. The energetic significance of basking is, however, largely unknown. We used biologging to measure the body temperature of free-ranging juvenile northern map turtles in Ontario, Canada. We measured the contribution of basking behaviour to the ability of turtles to reach their optimal body temperature for NER. We also used the predicted standard metabolic rate as a proxy to estimate the effects of basking on NER. Our results show that basking is essential for turtles to reach the optimal temperature for NER and suggest that basking behaviour allows turtles to increase their metabolic rate by 17.2 to 30.1%, which should translate into an even greater increase in NER. In addition, our results show that basking behaviour allows turtles to buffer the effects of climatic variations on their Tb and thus potentially on their energy budget. Collectively, our results suggest that basking behaviour has important ramifications for the energy budget, and by extension the fitness, of temperate-zone turtles.

Altered trophic pathway and parasitism in a native predator (Lepomis gibbosus) feeding on introduced prey (Dreissena polymorpha)

Populations of invasive species tend to have fewer parasites in their introduced ranges than in their native ranges and are also thought to have fewer parasites than native prey. This ‘release’ from parasites has unstudied implications for native predators feeding on exotic prey. In particular, shifts from native to exotic prey should reduce levels of trophically transmitted parasites. We tested this hypothesis in native populations of pumpkinseed sunfish (Lepomis gibbosus) in Lake Opinicon, where fish stomach contents were studied intensively in the 1970s, prior to the appearance of exotic zebra mussels (Dreissena polymorpha) in the mid-1990s. Zebra mussels were common in stomachs of present-day pumpkinseeds, and stable isotopes of carbon and nitrogen confirmed their importance in long-term diets. Because historical parasite data were not available in Lake Opinicon, we also surveyed stomach contents and parasites in pumpkinseed in both Lake Opinicon and an ecologically similar, neighboring lake where zebra mussels were absent. Stomach contents of pumpkinseed in the companion lake did not differ from those of pre-invasion fish from Lake Opinicon. The companion lake, therefore, served as a surrogate “pre-invasion” reference to assess effects of zebra mussel consumption on parasites in pumpkinseed. Trophically transmitted parasites were less species-rich and abundant in Lake Opinicon, where fish fed on zebra mussels, although factors other than zebra mussel consumption may contribute to these differences. Predation on zebra mussels has clearly contributed to a novel trophic coupling between littoral and pelagic food webs in Lake Opinicon.

Is There Such Thing as a Parasite Free Lunch? The Direct and Indirect Consequences of Eating Invasive Prey

As the number of invasive species increases globally, more and more native predators are reported to shift their diet toward invasive prey. The consequences of such diet shifts for the health of populations of native predators are poorly studied, but diet shifts are expected to have important parasitological and immunological consequences, ultimately affecting predator fitness. We reviewed evidence that diet shifts from native to invasive prey can alter parasite exposure directly and also indirectly affect immune functions via changes in condition and contaminant exposure. We highlight relevant conceptual and methodological tools that should be used for the design of experiments aimed at exploring important links between invasive prey and parasitism, contaminants and fitness of their native predators.

Sexual Dichromatism in the Northern Map Turtle, Graptemys geographica

Abstract Sexual dichromatism is common in many animal taxa, but little quantitative information on sexual dichromatism is available for turtles. We quantified sexual dichromatism in the postorbital spots of northern map turtles (Graptemys geographica) using reflectance spectrometry and examined the relationship between postorbital spot coloration and circulating testosterone among males. We found that the coloration of postorbital spots differs between the sexes, with adult males exhibiting brighter spots than adult females. However, adult males and juvenile females did not exibit siginficant differences in coloration, and testosterone levels did not explain the variation in postorbital spot coloration among males.

Does sexual bimaturation affect the cost of growth and the operational sex ratio in an extremely size-dimorphic reptile?

Abstract: Sexual bimaturation, an intersexual difference in age at maturity, is a consequence of sexual size dimorphism (SSD). Sexual bimaturation arises through intersexual differences in growth trajectories. In theory, differences in growth trajectories should bias the operational sex ratio in favour of the early-maturing sex. In addition, in animals with sexual bimaturation, the late-maturing sex always maintains a lower intrinsic rate of growth (k) that may be linked to the metabolic cost of growth. We studied growth, its relation to the operational sex ratio, and its metabolic cost in the extremely size-dimorphic northern map turtle. We found that females take twice as long as males to reach maturity and that females maintain higher absolute rates of growth but have a lower k. The estimated operational sex ratio was even in our study population, and estimates of annual mortality were similar between adult males and females. Based on respirometry, we found no evidence that fast-growing females incur a metabolic cost compared to non-growing males. Nomenclature: Le Sueur, 1817.

Infection of Yarrow's Spiny Lizards (Sceloporus jarrovii) by Chiggers and Malaria in the Chiricahua Mountains, Arizona

Abstract We measured prevalence of malaria infection and prevalence and intensity of chigger infection in Yarrows spiny lizards (Sceloporus jarrovii) from three sites in the Chiricahua Mountains of southeastern Arizona. Our primary objective was to compare parasite load among sites, sexes, and reproductive classes. We also compared our findings to those of previous studies on malaria and chiggers in S. jarrovii from the same area. Of lizards examined, 85 and 93% were infected by malaria and chiggers, respectively. Prevalence of malaria was two times higher than previously reported for the same area, while prevalence of chiggers was similar to previous findings. Intensity of chigger infection was variable among sites, but not among reproductive classes. The site with the highest intensity of chigger infection also had the most vegetative cover, suggesting that this habitat was more favorable for non-parasitic adult chiggers.

Dietary Reliance on Benthic Primary Production as a Predictor of Mercury Accumulation in Freshwater Fish and Turtles

The feeding ecology of a species can affect the transfer and accumulation of contaminants such as mercury (Hg). Modeling the accumulation of Hg through food webs can help identify which animals are likely to be burdened by elevated Hg concentrations. In lakes, most of the Hg is sequestered in the sediments. Therefore, species ultimately relying on benthic primary production may experience a greater trophic transfer of Hg relative to species that rely on pelagic primary production. This hypothesis was tested in a simple food web using muscle tissue collected from three species of fish (Lepomis gibbosus, Notropis heterodon, and Labidesthes sicculus) and blood from two species of turtles (Sternotherus odoratus and Chrysemys picta) that differ in reliance on benthic primary production. Averaged multiple linear regression models were used to predict Hg concentrations in the five consumers with respect to reliance on benthic primary production, while controlling for other factors known to influence Hg accumulation (sex, size, lake, species identity, and trophic level). A positive and significant relationship was found between Hg burden and dietary reliance on benthic primary production, animal length, trophic level, and species identity in fish. In turtles, the relationship between Hg burden and dietary reliance on benthic primary production was not significant, but trophic level, animal length, and species identity significantly influenced Hg burden. Overall, reliance on benthic primary production was an important predictor of Hg burden for fish, but not for turtles. Future attempts to model Hg accumulation in similar study systems and/or fish species should include dietary reliance on benthic primary production as a predictor variable.