Figure - available from: Frontiers in Ecology and Evolution
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Lack of association between the matrotrophy index per individual (MIind) and the individual index of fullness (IF) for 51 females of five fish species from the genus Poeciliopsis.
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The evolution of matrotrophy (post-fertilization maternal provisioning to developing embryos) has been explained through several hypotheses. Trexler and DeAngelis proposed in 2003 a theoretical model that defines the ecological conditions under which matrotrophy would be favored over lecithotrophy (pre-fertilization maternal provisioning). Accordin...
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... Therefore, it is necessary to test, at the microevolutionary scale, whether the evolution of higher degrees of placentotrophy across populations of a given species promotes greater sexual conflict, which in turn promotes the evolution of enhanced strategies to ensure paternity, similar to the pattern that has been detected at the interspecific scale. The genus Poeciliopsis is characterized by variations between and within species in the degrees of female placentotrophy, where a positive relationship between the amount of maternal supply to developing embryos after fertilization and the degree of placental complexity has been confirmed (Turner 1940;Thibault and Schultz 1978;Reznick et al. 2002;Kwan et al. 2015;Olivera-Tlahuel et al. 2019;Molina-Moctezuma et al. 2020;Saleh-Subaie et al. 2021). Therefore, it is reasonable to hypothesize that, within Poeciliopsis species, males have also experienced phenotypic changes associated with greater post-copulatory sexual selection and sperm competition in populations in which females have evolved higher levels of placentotrophy. ...
... To test our hypothesis, we used data on the degree of placentotrophy previously obtained by Saleh-Subaie et al. (2021) for the same populations that we examined in this study. The females used by Saleh-Subaie et al. (2021) and the males that we examined here were collected simultaneously from each population, between 2012 and 2013. The degree of placentotrophy is commonly quantified by means of the matrotrophy index (MI), which is calculated as the dry mass of the offspring at birth divided by the dry mass of the egg at fertilization (Skalkos et al. 2023). ...
Placentotrophy is a particular type of maternal provisioning to developing embryos, in which mothers actively provide nutrients via complex placental structures. Placentotrophy implies less pre-fertilization investment, resulting in a shift from pre-to post-copulatory sexual selection. This change can potentially result in a conflict between females and males. This phenomenon has been demonstrated at the interspecific level in viviparous fishes of the family Poeciliidae, in which males of species that lack placentotrophy have evolved traits related to pre-copulatory sexual selection such as coloration, ornaments, and courtship behavior. Placentotrophic species, on the other hand, have evolved traits associated with post-copulatory sexual selection such as long intromittent organs (gonopodium) and increased sexual coercion behavior. Here we test, for the first time at the intraspecific level, whether there is a similar relationship between a higher degree of female placentot-rophy and the evolution of male reproductive traits (larger testes and longer gonopodia) in three species of the genus Poeciliopsis (P. gracilis, P. infans, and P. prolifica). We observed a tendency towards longer gonopodia in males of P. gracilis as well as the largest testes of P. prolifica males in the populations with the highest degrees of placentotrophy. However, the statistical support for these findings was relatively weak. Therefore, we failed to support the hypothesis of a selective effect of female placentotrophy on male gonads and genitalia. We discuss other evolutionary forces that may have driven the observed intraspecific variation in male reproductive traits of Poeciliopsis fishes.
... Normal tables of development vary across species and thus, without consistent staging of both near fertilisation and near birth within a species or the equivalent between species, comparisons cannot be drawn. Most studies followed Haynes [44] embryonic staging, comparing stage four (blastocyst) to stage eleven (mature) [51,52], or Reznick [45], comparing stage two (uneyed) to stage six (very-late eyed/mature) [42,53]. Stage four and eleven from Haynes [44], equate to stage one and six in Reznick [45], respectively. ...
The source of embryonic nutrition for development varies across teleost fishes. A parentotrophy index (ratio of neonate: ovulated egg dry mass) is often used to determine provisioning strategy, but the methodologies used vary across studies. The variation in source and preservation of tissue, staging of embryos, and estimation approach impedes our ability to discern between methodological and biological differences in parentotrophy indices inter- and intra-specifically. The threshold value used to distinguish between lecithotrophy and parentotrophy (0.6–1) differs considerably across studies. The lack of a standardised approach in definition and application of parentotrophy indices has contributed to inconsistent classifications of provisioning strategy. Consistency in both methodology used to obtain a parentotrophy index, and in the classification of provisioning strategy using a threshold value are essential to reliably distinguish between provisioning strategies in teleosts. We discuss alternative methods for determining parentotrophy and suggest consistent standards for obtaining and interpreting parentotrophy indices.
