The predictability and magnitude of life‐history divergence to ecological agents of selection: a meta‐analysis in livebearing fishes

Abstract

Environments causing variation in age-specific mortality - ecological agents of selection - mediate the evolution of reproductive life-history traits. However, the relative magnitude of life-history divergence across selective agents, whether divergence in response to specific selective agents is consistent across taxa and whether it occurs as predicted by theory, remains largely unexplored. We evaluated divergence in offspring size, offspring number, and the trade-off between these traits using a meta-analysis in livebearing fishes (Poeciliidae). Life-history divergence was consistent and predictable to some (predation, hydrogen sulphide) but not all (density, food limitation, salinity) selective agents. In contrast, magnitudes of divergence among selective agents were similar. Finally, there was a negative, asymmetric relationship between offspring-number and offspring-size divergence, suggesting greater costs of increasing offspring size than number. Ultimately, these results provide strong evidence for predictable and consistent patterns of reproductive life-history divergence and highlight the importance of comparing phenotypic divergence across species and ecological selective agents.

Shared and unique patterns of phenotypic diversification along a stream gradient in two congeneric species

“…Likewise, increased fecundity and RA under high predation risk was reported for several poeciliids, including P. reticulata 2123, Brachyrhaphis rhabdophora 79, and G. hubbsi 66. This is in congruence with life-history theory, which predicts that when adult mortality rates are high relative to juvenile mortality rates, females increase reproductive effort, investing in as many offspring per clutch as possible to maximize fitness, even if this investment comes at the cost of producing smaller offspring2580.…”

“…Lowland rivers are slow-flowing, accumulate more nutrients, have higher photosynthetic primary production and thus, higher densities of guppies, and harbour an array of predatory species172021222324. Guppies show a repeated and predictable pattern of life-history divergence along this gradient, which was mainly interpreted as a consequence of differences in predation risk: under high predation (i.e., increased extrinsic mortality rates), guppy females produce more, but smaller offspring and allocate more resources to reproduction212325, while males mature at an earlier age and develop less conspicuous secondary sexual ornamentation2627. Several studies investigated guppy populations that are separated by waterfalls (allowing for a rather clear distinction between low- and high-predation habitats2123), but similar patterns of phenotypic differentiation were also found along a continuous gradient of predation28.…”

A mother’s legacy: the strength of maternal effects in animal populations

“…Nevertheless, when the maternal environment predicts the offspring environment, selection on the considerable phenotypic variation determined by maternal effects should favour their adaptive evolution. Exploring the genetic (McAdam et al ) and environmental (Marshall & Monro ; Tschirren et al ; Moore et al ) factors that promote and/or limit the evolutionary origins and maintenance of adaptive maternal effects will remain an exciting area for inquiry (e.g. Walsh et al ).…”

Independent lineages in a common environment: the roles of determinism and contingency in shaping the migration timing of even‐ versus odd‐year pink salmon over broad spatial and temporal scales

“…When non-parallelism is detected, its cause can be hard to determine (Travisano et al 1995;Langerhans & DeWitt 2004). One reason is that the supposedly replicate environmentsand presumed similar selection pressuresactually differ cryptically (e.g., Berner et al 2008;Kaeuffer et al 2012;Moore et al 2016). Alternatively, past evolutionary events might generate cryptic genomic variation that makes different 'replicate' lineages respond differently to the same selective regime (Travisano et al 1995;Langerhans & DeWitt 2004;Pfenninger et al 2015;Blount et al 2018).…”