Reproductive adaptations to reduce locomotor costs in viviparous fish (Poeciliidae)

Abstract

Historically, research on non-mammalian viviparity has suffered from anthropocentric views on reproduction, considering human (and mammalian) reproduction to be unique: live-bearing reproduction in non-mammalian species was considered a 'simple pattern' in which fertilized eggs developed and hatched inside the female [17,18]. Animals that lack 'true placentas', Figure 1-1. (next page) Phylogeny of the Poeciliidae indicating the level of matrotrophy and the presence of superfetation. Names depicted in bold indicate species used in this thesis. Boxes at the terminal ends indicate the presence (grey) or absence (white) of superfetation. Branch colour indicates a maximum likelihood reconstruction of maternal provisioning for natural log-transformed matrotrophy indices (MI), lnMI. Arrow indicates an MI of 1. The single egg-layer in the Poeciliidae family, Tomeurus gracilis, was excluded from this analysis. Adapted with permission from [67]. Figure 1-2. Overview of matrotrophy. A: Detail of an ovary of Phalloptychus januarius displaying matrotrophy. Arrowhead: maternal blood supply to a late-stage embryo. B: Frequency distribution of different levels of matrotrophy in Poeciliidae. Adapted from [28]. Inset: schematic overview of early-and late-stage embryos in lecithotrophic and matrotrophic species. C: The locomotor costs hypothesis predicts that the smaller oocytes at fertilization in matrotrophic fishes (B, inset) lead to a lower reproductive burden throughout pregnancy; the difference between the lecithotrophic and matrotrophic mode diminishes as pregnancy progresses.

Pregnancy affects flight behavior in big brown bats (Eptesicus fuscus)

“…Wingbeat rate was significantly higher in pregnant bats, and this likely remains true even when controlling for drop distance at larger sample sizes than we were able to achieve. Given that the pregnant bats had more difficulty achieving and maintaining UM, it stands to reason that they would increase their wingbeat rate to generate the power required for flight (Fleuren 2017; Fokidis and Risch 2008; Hayssen and Kunz 1996; McLean and Speakman 2000; Swartz et al 2012), which has been documented in prior work with bats undergoing horizontal, flapping flight (Hughes and Rayner 1991, 1993). This necessary power increase would be a regular, seasonal change that accompanies pregnancy-related increases in mass and wing loading, requiring a corresponding seasonal adjustment to flight behavior (Hughes and Rayner 1993).…”

“…Pregnancy involves morphological changes and increased body mass associated with decreased locomotor performance in terrestrial, aquatic, arboreal, and aerial species (Fleuren 2017; Smith and Young 2021); this reduces fitness by increasing predation risk and restricting ability to meet energetic demands (Fleuren 2017; Guillemette and Ouellet 2005; Hückstädt et al 2018; Kullberg et al 2002; Kullberg et al 2005; Lee et al 1996; Miles et al 2000; Noren et al 2011; Plaut 2002; Winfield and Townsend 1983). For example, gravid females demonstrate decreased locomotor speed and/or endurance compared to non-gravid females across a range of taxa (lizards: Miles et al 2000, Shine 1980; snakes: Seigel et al 1987; copepods: Winfield and Townsend 1983; scorpions: Shaffer and Formanowicz 1996; fish: Plaut 2002; dolphins: Noren et al 2011; seals: Hückstädt et al 2018; birds: Kullberg et al 2002; Kullberg et al 2005; Lee et al 1996; Videler et al 1988; bats: Hughes and Rayner 1991, 1993, McLean and Speakman 2000).…”

“…One way to partially mitigate the impact of increased wing loading is to increase wingbeat frequency, thus generating more power (Fleuren 2017; Swartz et al 2012). This strategy has been noted for some artificially loaded birds and bats, as well as pregnant bats in a small flight room, which increase wingbeat rate and decrease flight speed (Hughes and Rayner 1991, 1993; Pennycuick et al 1989; Videler et al 1988).…”