Coasting in live-bearing fish: the drag penalty of being pregnant

Abstract

<jats:p>Swimming performance of pregnant live-bearing fish is presumably constrained by the additional drag associated with the reproductive burden. Yet, it is still unclear how and to what extent the reproductive investment affects body drag of the females. We examined the effect of different levels of reproductive investment on body drag. The biggest measured increase in body volume due to pregnancy was about 43%, linked to a wetted area increase of about 16% and 69% for the frontal area. We printed three-dimensional models of live-bearing fish in a straight body posture representing different reproductive allocation (RA) levels. We measured the drag and visualized the flow around these models in a flow tunnel at different speeds. Drag grew in a power fashion with speed and exponentially with the increase of RA, thus drag penalty for becoming thicker was relatively low for low speeds compared to high ones. We show that the drag increase with increasing RA was most probably due to bigger regions of flow separation behind the enlarged belly. We suggest that the rising drag penalty with an increasing RA, possibly together with pregnancy-related negative effects on muscle- and abdominal bending performance, will reduce the maximum swimming speed.</jats:p>

Predator Environment Does Not Predict Life History in the Morphologically Constrained Fish Alfaro cultratus (Cyprinodontiformes: Poeciliidae)

“…In the family Poeciliidae, fishes invest more in offspring when predators are present than when they are absent; however, this investment comes at a cost of decreased swimming performance (Ghalambor et al, 2004). Thus the optimal morphology for swimming performance and the optimal morphology for reproduction can be in conflict (Zúñiga-Vega et al, 2007;Wesner et al, 2011;Hassell et al, 2012;Ingley et al, 2016;Quicazan-Rubio et al, 2019). Selective pressures acting on morphology can limit the optimal adaptation in life history or vice versa in a given environment.…”

Predation risk shapes the degree of placentation in natural populations of live‐bearing fish

“…). A lower RA and streamlined body shape are associated with a reduced drag on the female body (Quicazan‐Rubio et al 2019), higher sustained swimming performance (Plaut 2002), improved fast‐start escape response (Ghalambor et al 2004; Fleuren et al 2019), and enhanced survival probability (Walker et al 2005; Plath et al 2011; Laidlaw et al 2014).…”

“…In high predation environments, females of the placental P. retropinna reduced their reproductive allotment, notably without reducing the size or number of offspring at birth. This is likely to be advantageous for the mother, as the decreased reproductive allotment improves her locomotor performance (Plaut 2002; Ghalambor et al 2004; Fleuren et al 2019; Quicazan‐Rubio et al 2019) and survival probability in high predation environments (Plath et al 2011; Laidlaw et al 2014). This life‐history adaptation is however unavailable to lecithotrophic species.…”

Rheotaxis Response Based on Sexual Dimorphism in the Green Swordtail Fish, Xiphophorus hellerii

“…Although the lipid storage is useful for pelagic fish, such as the great white shark (Carcharodon carcharias) in terms of buoyancy setting as well as a source of energy during long migration (Raye et al, 2013), it seems that the same mechanisms do not occur in sedentary freshwater fish. Quicazan-Rubio et al (2019) reported that the guppy fish (family: Poeciliidae) had increased body volume up to 43%, as well, as their frontal body area has expanded up to 69% during the gravid period, causing the fish movement in flowing water becomes much heavier due to the greater thrust of the flowing water against the enlarged body. Besides, the abdomen and muscles' flexibility will be decreased during the gravid period, which results in the decreasing of the maximum speed of the fish when swimming (Quicazan-Rubio et al, 2019).…”