Replicated Functional Evolution in Cichlid Adaptive Radiations.

AbstractAdaptive radiations highlight the mechanisms by which species and traits diversify and the extent to which these patterns are predictable. We used 1,110 high-speed videos of suction feeding to study functional and morphological diversification in 300 cichlid species from three African Great Lake radiations of varying ages (Victoria, Malawi, and Tanganyika) and an older, spatially dispersed continental radiation in the Neotropics. Among African radiations, standing diversity was reflective of time. Morphological and functional variance in Lake Victoria, the youngest radiation, was a subset of that within Lake Malawi, which itself was nested within the older Tanganyikan radiation. However, functional diversity in Neotropical cichlids was often lower than that in Lake Tanganyika, despite being much older. These two radiations broadly overlapped, but each diversified into novel trait spaces not found in the youngest lake radiations. Evolutionary rates across radiations were inversely related to age, suggesting extremely rapid trait evolution at early stages, particularly in lake radiations. Despite this support for early bursts, other patterns of trait diversity were inconsistent with expectations of adaptive radiations. This work suggests that cichlid functional evolution has played out in strikingly similar fashion in different radiations, with contingencies eventually resulting in lineage-specific novelties.

Local adaptation of antipredator behaviors in populations of a temperate reef fish.

The temperament of animals can vary among individuals and among populations, but it is often unclear whether spatial variation in temperament is the result of acclimation to local environmental conditions or genetic adaptation to spatial differences in natural selection. This study tested whether populations of a marine fish that experience different levels of mortality and fishing exhibited local adaptation in behaviors related to predator avoidance and evasion. First, we measured variation in reactivity to perceived risk in wild populations of black surfperch (Embiotoca jacksoni). We compared flight initiation distances (FID) between populations with significantly different mortality rates. After finding that FID values were substantially lower in the low-risk locations, we tested for local adaptation by rearing lab-born offspring from both high- and low-risk populations in a common environment before measuring their behavior. Lab-reared offspring from high- and low-risk populations exhibited significant differences in several behaviors related to reactivity. Between 23 and 43% of the total variation in behaviors we measured could be attributed to source population. These results thus suggest that a substantial amount of spatial variation in behaviors related to predator evasion may represent local adaptation. In addition, behaviors we measured had an average, broad-sense heritability of 0.24, suggesting that the behavioral tendencies of these populations have some capacity to evolve further in response to any changes in selection.

Effects of size and sex on the courting success and foraging behaviour of Embiotoca jacksoni.

To test life-history theory that body size and sex should influence how animals allocate time to foraging versus reproductive activities, we measured the effects of size and sex on courting success and foraging behaviour of black surfperch Embiotoca jacksoni off Santa Catalina Island, southern California. Observations of focal fish were made while snorkelling, during which the length of each fish (estimated to the nearest cm), total duration of courting encounters and foraging rates were recorded. We made observations during and outside the mating season. Courtship occurred only between pairs and its duration increased with the size of both the male and female. Although males would court females that were smaller or larger than themselves, pairs that were closely matched in size had long courting sessions, whereas those that differed considerably in size courted only briefly. Small fish foraged more than larger fish, both during and outside the mating season. Males and females foraged at similar rates outside of the mating season, but during the mating season males reduced their foraging rates to less than half that seen outside of the mating season, whereas females continued to forage at the same rate. This decrease in foraging rate of males during the mating season was seen in all sizes of males but was proportionally greatest in the largest males. These observations indicate that males trade off time spent on foraging for time spent courting during the mating season, whereas females do not.