Adaptive Phenotypic Plasticity and Genetics of Larval Life Histories in Two Rana Temporaria Populations

Abstract

Phenotypic plasticity provides means for adapting to environmental unpredictability. In terms of accelerated development in the face of pond-drying risk, phenotypic plasticity has been demonstrated in many amphibian species, but two issues of evolutionary interest remain unexplored. First, the heritable basis of plastic responses is poorly established. Second, it is not known whether interpopulational differences in capacity to respond to pond-drying risk exist, although such differences, when matched with differences in desiccation risk would provide strong evidence for local adaptation. We investigated sources of within- and among-population variation in plastic responses to simulated pond-drying risk (three desiccation treatments) in two Rana temporaria populations originating from contrasting environments: (1) high desiccation risk with weak seasonal time constraint (southern population); and (2) low desiccation risk with severe seasonal time constraint (northern population). The larvae originating from the environment with high desiccation risk responded adaptively to the fast decreasing water treatment by accelerating their development and metamorphosing earlier, but this was not the case in the larvae originating from the environment with low desiccation risk. In both populations, metamorphic size was smaller in the high-desiccation-risk treatment, but the effect was larger in the southern population. Significant additive genetic variation in development rate was found in the northern and was nearly significant in the southern population, but there was no evidence for genetic variation in plasticity for development rates in either of the populations. No genetic variation for plasticity was found either in size at metamorphosis or growth rate. All metamorphic traits were heritable, and additive genetic variances were generally somewhat higher in the southern population, although significantly so in only one trait. Dominance variances were also significant in three of four traits, but the populations did not differ. Maternal effects in metamorphic traits were generally weak in both populations. Within-environment phenotypic correlations between larval period and metamorphic size were positive and genetic correlations negative in both populations. These results suggest that adaptive phenotypic plasticity is not a species-specific fixed trait, but evolution of interpopulational differences in plastic responses are possible, although heritability of plasticity appears to be low. The lack of adaptive response to desiccation risk in northern larvae is consistent with the interpretation that selection imposed by shorter growing season has favored rapid development in north (approximately 8% faster development in north as compared to south) or a minimum metamorphic size at the expense of phenotypic plasticity.

Physiological, Behavioral and Maternal Factors That Contribute to Size Variation in Larval Amphibian Populations

“…These individual traits were partly associated familial differences in growth rate, but more so by differences in their hatching date, which could result from variance in genetics, maternal effects, and environmental conditions experienced by eggs within a clutch. This is consistent with amphibian studies comparing populations which have shown that genetic variance to some extent underlies phenotypic variation in growth rates [11], [44]. However, within populations larval growth appears to be largely determined by environmental factors coupled with the influence of maternal effects [8], [11], [44], [45].…”

“…This is consistent with amphibian studies comparing populations which have shown that genetic variance to some extent underlies phenotypic variation in growth rates [11], [44]. However, within populations larval growth appears to be largely determined by environmental factors coupled with the influence of maternal effects [8], [11], [44], [45]. In amphibians, maternal effects can include egg size, clutch size and placement within a pond.…”

Cannibalism and activity rate in larval damselflies increase along a latitudinal gradient as a consequence of time constraints

“…Note that at higher latitudes a long day length the weeks before and after summer solstice, although it allows for more foraging and growth (since more hours of light are available), actually is a cue that signals seasonal time constraints. Such constraints are common in organisms with complex life cycles, such as insects and amphibians [24–26]. Seasonal time constraints usually increase with latitude and altitude because the time available for growth and development decrease with these variables [27].…”

Australian black field crickets show changes in neural gene expression associated with socially-induced morphological, life-history, and behavioral plasticity

“…It is specifically this life-history plasticity that is well studied both theoretically and empirically [1, 4] in ecological and evolutionary organisms. Decades of research on life-history driven plasticity has resulted in a strong understanding of the ecological triggers [5–8], adaptive benefits [9–11] and factors necessary for the evolution of such developmentally plastic tactics [12–14]. …”