Role of sexual imprinting in assortative mating and premating isolation in Darwin’s finches

Abstract

Global biodiversity is being degraded at an unprecedented rate, so it is important to preserve the potential for future speciation. Providing for the future requires understanding speciation as a contemporary ecological process. Phylogenetically young adaptive radiations are a good choice for detailed study because diversification is ongoing. A key question is how incipient species become reproductively isolated from each other. Barriers to gene exchange have been investigated experimentally in the laboratory and in the field, but little information exists from the quantitative study of mating patterns in nature. Although the degree to which genetic variation underlying mate-preference learning is unknown, we provide evidence that two species of Darwin’s finches imprint on morphological cues of their parents and mate assortatively. Statistical evidence of presumed imprinting is stronger for sons than for daughters and is stronger for imprinting on fathers than on mothers. In combination, morphology and species-specific song learned from the father constitute a barrier to interbreeding. The barrier becomes stronger the more the species diverge morphologically and ecologically. It occasionally breaks down, and the species hybridize. Hybridization is most likely to happen when species are similar to each other in adaptive morphological traits, e.g., body size and beak size and shape. Hybridization can lead to the formation of a new species reproductively isolated from the parental species as a result of sexual imprinting. Conservation of sufficiently diverse natural habitat is needed to sustain a large sample of extant biota and preserve the potential for future speciation.

Adult sex ratio influences mate choice in Darwin’s finches

“…A previous study of the mating patterns of the finch species on Daphne has provided evidence in support of a hypothesis of mate choice based on parental imprinting (41). According to the hypothesis, the choice of a mate is influenced by early experience of parental morphology (41)(42)(43)(44)(45). Females are expected to choose males with morphological features close to their own parents' morphology under conditions that are favorable for expressing such choice.…”

“…A male-biased sex ratio implies increased opportunity for females to choose high-quality males (39). A previous study of the mating patterns of the finch species on Daphne has provided evidence in support of a hypothesis of mate choice based on parental imprinting (41). According to the hypothesis, the choice of a mate is influenced by early experience of parental morphology (41)(42)(43)(44)(45).…”

“…When offspring imprint on their parents, they are expected to choose mates morphologically like their parents(41). Since offspring resemble their parents (heritability = 0.7-0.8), imprinting should lead to positive assortative mating(41).…”

How phenotypic matching based on neutral mating cues enables speciation in locally adapted populations

“…Experiments have shown that female but not male cichlids in the genera Pundamilia and Mbipia imprint on their mothers' phenotypes (Verzijden & ten Cate, ; Verzijden, Korthof, & Cate, ; Verzijden, Zwinkels, & Cate, )—as in case (b) above —raising the intriguing possibility that imprinting is part of the explanation of the spectacular speciosity of cichlids in the African rift valley lakes. Mate choice in Darwin's finches too is largely determined by sexual imprinting (Grant & Grant, ).…”

Darwin’s finches choose parent lookalikes as mates

“…For decades, evolutionary biologists have sought to understand the links between an individual's choice of mate and reproductive isolation between populations and species 1 . Writing in Proceedings of the National Academy of Sciences, Grant and Grant 2 provide evidence suggesting that two species of Darwin's finch learn features of their parents early in life and use this knowledge to inform their choice of mate in adulthood, a process known as sexual imprinting. Their study raises fascinating questions about the roles of learning and genetics in mate choice, and how matings between similar individuals (assortative mating) drive the evolution of new species.…”