Life History Divergence in Livebearing Fishes in Response to Predation: Is There a Microevolution to Macroevolution Barrier?

Abstract

A central problem in evolutionary biology is to determine whether adaptive phenotypic variation within species (microevolution) ultimately gives rise to new species (macroevolution). Predation environment can select for trait divergence among populations within species. The implied hypothesis is that the selection resulting from predation environment that creates population divergence within species would continue across the speciation boundary such that patterns of divergence after speciation would be a magnified accumulation of the trait variation observed before speciation. In this paper, we test for congruence in the mechanisms of microevolution and macroevolution by comparing the patterns of life history divergence among three closely related species of the livebearer genus Brachyrhaphis (Poeciliidae), namely B. rhabdophora, B. roseni, and B. terrabensis. Within B. rhabdophora, populations occur in either predator or predator-free environments, and have been considered to be at a nascent stage of speciation. Sister species B. roseni and B. terrabensis are segregated into predator and predator-free environments, respectively, and represent a post-speciation comparison. Male and female size at maturity, clutch size, and offspring size (and to a lesser extent reproductive allocation) all diverged according to predation environment and differences were amplified through evolutionary time, i.e., across the speciation boundary. Variation observed among nascent species differentiated by predation environment is a good predictor of variation among established species differentiated by predation environment. We found no evidence for different processes or different levels of selection acting across the speciation boundary, suggesting that macroevolution in these species can be understood as an accumulation of micro-evolutionary changes.

Predator Environment Does Not Predict Life History in the Morphologically Constrained Fish Alfaro cultratus (Cyprinodontiformes: Poeciliidae)

“…Variation in actual mortality rates among localities could prove problematic to our simple placement of populations into either high or low mortality groups. This said, such categories have proved effective at predicting mortality rates in other systems (Johnson and Belk, 2001;Johnson and Zúñiga-Vega, 2009;Ingley et al, 2014;Belk et al, 2020). Lack of phenotypic divergence might also be attributed to gene flow between populations that can limit the ability of populations to adapt to selective pressures in their environment and therefore decrease differences between populations (Storfer, 1999).…”

Predation and Resource Availability Interact to Drive Life-History Evolution in an Adaptive Radiation of Livebearing Fish

“…Livebearing fishes (family Poeciliidae), such as guppies, mollies, swordtails, and mosquitofish, have been at the forefront of the development of life-history theory (e.g., Reznick and Endler, 1982;Reznick et al, 1990Reznick et al, , 2002Johnson, 2001;Johnson and Belk, 2001;Bronikowski et al, 2002;Jennions and Telford, 2002;Jennions et al, 2006;Riesch et al, 2014Riesch et al, , 2015Moore et al, 2016;Belk et al, 2020;Santi et al, 2020). One especially powerful model system of livebearing fish is the post-Pleistocene radiation of Bahamas mosquitofish (Gambusia hubbsi), as the system offers the opportunity to isolate the effects of predation risk and resource availability on life-history trait evolution.…”

Predators as Agents of Selection and Diversification

“…This classic pattern of divergent selective pressures leading to evolutionary diversification reinforces the importance of selection as a driver of evolutionary change. Our paper [58] builds on this idea by showing that evolutionary diversification driven by the presence or absence of predators within the livebearing fish species Brachyrhaphis rhabdophora is mirrored in the continued evolutionary diversification in two other Brachyrhaphis fish species that have already undergone speciation. In essence, this work suggests that predation itself has likely contributed to the formation of two new species.…”