Authors: Evatt Chirgwin, Dustin J  Marshall, Carla M Sgrò, and Keyne Monro

Published in: Evolutionary Applications, volume 10, issue 3 (March 2017)

Abstract

Mounting research considers whether populations may adapt to global change based on additive genetic variance in fitness. Yet selection acts on phenotypes, not additive genetic variance alone, meaning that persistence and evolutionary potential in the near term, at least, may be influenced by other sources of fitness variation, including nonadditive genetic and maternal environmental effects. The fitness consequences of these effects, and their environmental sensitivity, are largely unknown.

Here, applying a quantitative genetic breeding design to an ecologically important marine tubeworm, we examined nonadditive genetic and maternal environmental effects on fitness (larval survival) across three thermal environments.

We found that these effects are nontrivial and environment dependent, explaining at least 44% of all parentally derived effects on survival at any temperature and 96% of parental effects at the most stressful temperature. Unlike maternal environmental effects, which manifested at the latter temperature only, nonadditive genetic effects were consistently significant and covaried positively across temperatures (i.e., parental combinations that enhanced survival at one temperature also enhanced survival at elevated temperatures).

Thus, while nonadditive genetic and maternal environmental effects have long been neglected because their evolutionary consequences are complex, unpredictable, or seen as transient, we argue that they warrant further attention in a rapidly warming world.

Citation

Chirgwin E, Marshall DJ, Sgrò CM, Monro K (2016) The other 96%: Can neglected sources of fitness variation offer new insights into adaptation to global change? Evolutionary Applications, 10(3) PDF 445 KB doi: 10.1111/eva.12447

Authors: Colin Olito, Dustin J Marshall, and Tim Connallon

Published in: The American Naturalist, volume 189, number 2 (February 2017)

Abstract

Reproductive phenology is a crucial life-history trait that evolves in response to external environmental conditions and frequency- and density-dependent interactions within species.

Broadcast spawners — which represent a large fraction of aquatic biodiversity — evolve phenologies that balance strong density-dependent fertilization success against abiotic environmental conditions that are required for successful reproduction. The overall balance between these processes may be particularly complex in dioecious species, where selection on reproductive timing potentially differs between the sexes.

Here, we develop a population genetic model of reproductive phenology in a dioecious broadcast spawning species and show that environmental variability and density-dependent fertilization dynamics naturally give rise to profound sex differences in selection on gamete release strategies.

The frequency-dependent nature of sperm competition generates sexually antagonistic selection on reproductive timing and facilitates the maintenance of genetic variation in phenological traits. Selection in females favors monomorphic spawning phenologies that maximize net fertilization success and offspring survival across environmental conditions, whereas selection in males often favors polymorphic phenologies that are primarily shaped by sperm competition.

Our model helps explain several well-documented empirical observations in aquatic species, including high intraspecific variance of reproductive phenologies, sex-specific spawning phenologies, and spawning during environmentally suboptimal times.

Citation

Olito C, Marshall DJ, Connallon T (2017) The evolution of reproductive phenology in broadcast spawners and the maintenance of sexually antagonistic polymorphism, The American Naturalist, 189(2) PDF 717 KB, doi:10.1086/690010