Turtle hatchlings show behavioral types that are robust to developmental manipulations

There can be substantial variation among individuals within a species in how they behave, even under similar conditions; this pattern is found in many species and across taxa. However, the mechanisms that give rise to this behavioral variation are often unclear. This study investigated the influence of environmental manipulations during development on behavioral variation in hatchlings of the red-eared slider turtle (Trachemys scripta). First, we examined the effects of three manipulations during incubation (estrone sulfate exposure, corticosterone exposure, and thermal fluctuations) on hatchling righting response and exploration. Second, we determined whether hatchlings showed consistent differences (i.e. behavioral types) in their righting response and exploration across days and months, and whether these behaviors were correlated with one another. Finally, we examined whether righting response was predictive of ecologically relevant behaviors such as habitat choice and dispersal. Hatchling behavior was robust to our early manipulations; none of the pre-hatch treatments affected later behavior. There were significant clutch effects, which due to the split-clutch design suggests genetic underpinnings and/or maternal effects. We found evidence for behavioral types in turtles; both righting response and exploration were strongly repeatable and these behaviors were positively correlated. Righting response was not predictive of dispersal ability in the field, necessitating a revision in the general interpretations of righting response as a proxy for dispersal ability in turtles. Thus, turtle hatchlings show consistent behavioral differences that are robust to early developmental manipulations, and while not necessarily predictive of dispersal, these behavioral types can have important consequences throughout ontogeny.

Speciation in killifish and the role of salt tolerance

Species pairs whose distributions are tied to environmental conditions provide intriguing candidates for the study of ecological speciation. Here, we examine the role that adaptation to salinity has played in the divergence between two closely related species, Lucania goodei and Lucania parva, whose distributions reflect salinity (L. goodei- fresh water, L. parva- euryhaline). We first tested whether these two species display local adaptation and, subsequently, tested for ecological, genic and behavioural isolation by performing crosses within and between L. goodei and L. parva and raising offspring under various salinities. We found strong evidence for differential adaptation to salinity and also for behavioural isolation where animals preferentially mated with conspecifics over heterospecifics. However, we found no evidence for F1 hybrid inviability. We discuss the general lack of evidence for genic isolation in teleost fish and whether this is a real phenomenon or simply a reflection of experimental design.