A variance partitioning perspective of assortative mating: Proximate mechanisms and evolutionary implications

Abstract

Assortative mating occurs when paired individuals of the same population are more similar than expected by chance. This form of non‐random assortment has long been predicted to play a role in many evolutionary processes because assortatively mated individuals are assumed to be genetically similar. However, this assumption may always hold for labile traits, or traits that are measured with error. For such traits, there is a variety of proximate mechanisms that can drive phenotypic resemblance between mated partners that, notably, have very different evolutionary repercussions. Bettering our understanding of the role of assortative mating in evolution will thus require insight into its proximate causes. To date, empirical research remains sparse, especially when for labile traits. This special issue aims to stimulate such research while promoting the usage and development of statistical approaches allowing the quantification of the relative roles of alternative proximate mechanisms causing assortative mating. To this end, we first describe how the phenotypic covariance between mated partners can be usefully partitioned into components that capture one or several of five distinct mechanisms. We then demonstrate why the importance of mechanisms causing genetic covariance between the traits of partners may often be overestimated. Finally, we detail how the evolutionary causes and consequences of the diverse mechanisms may be identified.

Morphological variation and reproductive isolation in the Hetaerina americana species complex

“…For example, body size was previously reported as a strong premating barrier in different animal groups 26 – 28 . In this context, male assortative mating by size has been described in H. americana sensu lato 29 , and even though we cannot ensure interspecific discrimination of females based on their size, it has been widely recognized that assortative mating can promote or reinforce divergence even in incipient species and in the presence of gene flow 30 , 31 . Assortative mating in males of H. americana y H. calverti could have two causes: first, males prefer mates with specific trait values, in this case larger females because they may be more fertile (and not because they discriminate between species).…”

Linking personality traits and reproductive success in common marmoset (Callithrix jacchus)

“…Thus, the personality pair composition in our study population does not necessarily reflect the situation in the wild. Future studies should examine the variation in pair personality composition in wild common marmosets and the mechanisms underlying it, such as mate choice, social conformity or stratification of personality types in the space or time 67 . Studies on captive fish 68 , birds 69 , and mammals 70 with biparental care have shown that females choose partners based on their personality, and these pairs have higher reproductive success.…”

Does fluctuating selection maintain variation in nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius)?

“…Among‐individual differences in nest defense could also be maintained through nonrandom mating, whereby the fitness of particular combinations of parent behavioral types (i.e., individuals mean phenotypic value for a behavioral trait) have higher success because they are behaviorally and/or genetically more compatible (Class & Dingemanse, 2022 ; Jiang et al, 2013 ; Tregenza & Wedell, 2000 ). Positive assortative mating (hereafter referred to as “assortative mating”) based on behavioral type can contribute to the maintenance of among‐individual differences if pairing with individuals of similar phenotype (i.e., high aggression with high aggression, low aggression with low aggression) has a net positive fitness outcome (Jiang et al, 2013 ; Schuett et al, 2010 ; Tregenza & Wedell, 2000 ).…”

“…Among-individual differences in nest defense could also be maintained through nonrandom mating, whereby the fitness of particular combinations of parent behavioral types (i.e., individuals mean phenotypic value for a behavioral trait) have higher success because they are behaviorally and/or genetically more compatible (Class & Dingemanse, 2022;Jiang et al, 2013;Tregenza & Wedell, 2000).…”