Evidence that genetic compatibility underpins female mate choice in a monandrous amphibian

The Sixth Mass Extinction and Amphibian Species Sustainability Through Reproduction and Advanced Biotechnologies, Biobanking of Germplasm and Somatic Cells, and Conservation Breeding Programs (RBCs)

Primary themes in intergenerational justice are a healthy environment, the perpetuation of Earth's biodiversity, and the sustainable management of the biosphere. However, the current rate of species declines globally, ecosystem collapses driven by accelerating and catastrophic global heating, and a plethora of other threats preclude the ability of habitat protection alone to prevent a cascade of amphibian and other species mass extinctions. Reproduction and advanced biotechnologies, biobanking of germplasm and somatic cells, and conservation breeding programs (RBCs) offer a transformative change in biodiversity management. This change can economically and reliably perpetuate species irrespective of environmental targets and extend to satisfy humanity's future needs as the biosphere expands into space. Currently applied RBCs include the hormonal stimulation of reproduction, the collection and refrigerated storage of sperm and oocytes, sperm cryopreservation, in vitro fertilization, and biobanking of germplasm and somatic cells. The benefits of advanced biotechnologies in development, such as assisted evolution and cloning for species adaptation or restoration, have yet to be fully realized. We broaden our discussion to include genetic management, political and cultural engagement, and future applications, including the extension of the biosphere through humanity's interplanetary and interstellar colonization. The development and application of RBCs raise intriguing ethical, theological, and philosophical issues. We address these themes with amphibian models to introduce the Multidisciplinary Digital Publishing Institute Special Issue, The Sixth Mass Extinction and Species Sustainability through Reproduction Biotechnologies, Biobanking, and Conservation Breeding Programs.

Parental kinship coefficient but not paternal coloration predicts early offspring growth in lake char

The 'good genes' hypotheses of sexual selection predict that females prefer males with strong ornaments because they are in good health and vigor and can afford the costs of the ornaments. A key assumption of this concept is that male health and vigor are useful predictors of genetic quality and hence offspring performance. We tested this prediction in wild-caught lake char (Salvelinus umbla) whose breeding coloration is known to reveal aspects of male health. We first reanalyzed results from sperm competition trials in which embryos of known parenthood had been raised singly in either a stress- or non-stress environment. Paternal coloration did not correlate with any measures of offspring performance. However, offspring growth was reduced with higher kinship coefficients between the parents. To test the robustness of these first observations, we collected a new sample of wild males and females, used their gametes in a full-factorial in vitro breeding experiment, and singly raised about 3000 embryos in either a stress- or non-stress environment (stress induced by microbes). Again, paternal coloration did not predict offspring performance, while offspring growth was reduced with higher kinship between the parents. We conclude that, in lake char, the genetic benefits of mate choice would be strongest if females could recognize and avoid genetically related males, while male breeding colors may be more relevant in intra-sexual selection.

Multiple phenotypic traits predict male mating success in a critically endangered frog

Abstract

Complex sexual signals spanning multiple sensory modalities may be common in nature, yet few studies have explored how combinations of phenotypic traits influence male attractiveness and mating success. Here, we investigate whether combinations of multiple male phenotypic traits (both within and across sensory modalities) predict male mating and fertilization success in the critically endangered southern corroboree frog, Pseudophryne corroboree. We conducted breeding trials in a standardized captive environment where females were given the opportunity to choose between multiple males over the duration of the breeding season. For each male, we measured multiple call traits, aspects of coloration, body size, and age. We found that complex interactions between multiple traits best predicted male mating and fertilization success. In general, males with lower call frequency, lower call rate, and shorter call duration had the highest mating and fertilization success. Fertilization success was additionally linked to male body size and age. These findings suggest that female P. corroboree select mates based on a suite of acoustic traits, adding to a growing body of evidence that females use multiple traits to assess male quality. Our results also suggest that females may combine information from multiple signals non-additively. Moreover, our results imply that females gain direct fertility benefits from their mate choice decisions. We argue that understanding female mate choice based on various signals across multiple sensory modalities has important implications for the integration of mate choice into conservation breeding programs and needs to be considered when developing behavior-based captive breeding strategies.

Significance statement

Sexual signals are often highly complex, yet we know little about how multiple signal components both within and across various sensory modalities predict male mating success. We investigated whether combinations of multiple phenotypic traits (within and across sensory modalities) predicted male breeding success in threatened corroboree frogs. We conducted captive breeding trials in a homogeneous environment, where females could choose between multiple males over the duration of a single breeding season. We found that interactions between multiple male traits predicted mating and fertilization success. Males with lower call frequency, call rate, and duration had higher mating success. Fertilization success was also linked to acoustic signals, body size, and age. Understanding mate choice for multiple traits further elucidates the complexity of female mate choice. This study is one of the first to consider the conservation implications of multimodal signaling in mate choice.

Sexual selection and the ascent of women: Mate choice research since Darwin

Darwin's theory of sexual selection fundamentally changed how we think about sex and evolution. The struggle over mating and fertilization is a powerful driver of diversification within and among species. Contemporaries dismissed Darwin's conjecture of a "taste for the beautiful" as favoring particular mates over others, but there is now overwhelming evidence for a primary role of both male and female mate choice in sexual selection. Darwin's misogyny precluded much analysis of the "taste"; an increasing focus on mate choice mechanisms before, during, and after mating reveals that these often evolve in response to selection pressures that have little to do with sexual selection on chosen traits. Where traits and preferences do coevolve, they can do so whether fitness effects on choosers are positive, neutral, or negative. The spectrum of selection on traits and preferences, and how traits and preferences respond to social effects, determine how sexual selection and mate choice influence broader-scale processes like reproductive isolation and population responses to environmental change.

Genetic incompatibility of the reproductive partners: an evolutionary perspective on infertility

In natural fertilisation, the female reproductive tract allows only a strictly selected sperm subpopulation to proceed in the vicinity of an unfertilised oocyte. Female-mediated sperm selection (also known as cryptic female choice (CFC)) is far from a random process, which frequently biases paternity towards particular males over others. Earlier studies have shown that CFC is a ubiquitous phenomenon in the animal kingdom and often promotes assortative fertilisation between genetically compatible mates. Here, I demonstrate that CFC for genetic compatibility likely also occurs in humans and is mediated by a complex network of interacting male and female genes. I also show that the relative contribution of genetic compatibility (i.e. the male-female interaction effect) to reproductive success is generally high and frequently outweighs the effects of individual males and females. Together, these facts indicate that, along with male- and female-dependent pathological factors, reproductive failure can also result from gamete-level incompatibility of the reproductive partners. Therefore, I argue that a deeper understanding of these evolutionary mechanisms of sperm selection can pave the way towards a more inclusive view of infertility and open novel possibilities for the development of more personalised infertility diagnostics and treatments.