The volitional travel speed varies with reproductive state in mature female brown trout Salmo trutta

Repeatability of locomotor performance and of morphology – locomotor performance relationships

There is good evidence that natural selection drives the evolution of locomotor performance, but the processes that generate among individual variation in locomotion, the substrate upon which selection acts, are relatively poorly understood. We measured prolonged swimming performance, Ucrit, and morphology in a large cohort (n=461) of wildtype zebrafish, Danio rerio, at ∼6 months and again at ∼9 months. Using mixed model analyses to estimate repeatability as the intraclass correlation coefficient, we determined that Ucrit was significantly repeatable (r = 0.55; 95% CI: 0.45 -0.64). Performance differences between the sexes (males 12% faster than females) and changes with age (decreasing 0.07% per day) both contributed to variation in Ucrit and, therefore, the repeatability estimate. Accounting for mean differences between sexes within the model decreased the estimate of Ucrit repeatability to 21% below the naïve estimate, while fitting age in the models increased the estimate to 14% above the naïve estimate. Greater consideration of factors such as age and sex is therefore necessary for the interpretation of performance repeatability in wild populations. Body shape significantly predicted Ucrit in both sexes in both assays, with the morphology – performance relationship significantly repeatable at the population level. However, morphology was more strongly predicative of performance in older fish, suggesting a change in the contribution of morphology relative to other factors such as physiology and behaviour. The morphology – performance relationship changed with age to a greater extent in males than females.

Sexually dimorphic morphology and swimming performance relationships in wild-type zebrafish Danio rerio

This study compared prolonged swimming performance (Ucrit ) between male and female Danio rerio, and characterized how body shape was associated with this performance measure in each sex. When swimming in small (n = 6) mixed-sex groups at 28 °C, males swam, on average, over 10 cm s(-1) faster than females despite being significantly smaller. Body shape was sexually dimorphic, with males and females exhibiting small, but statistically significant differences in most aspects of body shape. Body shape explained 18 and 43% of the variation in Ucrit among males and females. In general, effects of body shape on swimming performance appeared to be sex limited, whereby different aspects of body shape affected performance in each sex, although the contribution of the distance between pelvic and anal fins to swimming performance was weakly sexually antagonistic.

Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus)

Constraints on locomotion could be an important component of the cost of reproduction as carrying an increased load associated with eggs or developing fetuses may contribute to decreased locomotor performance for females across taxa and environments. Diminished performance could increase susceptibility to predation, yet the mechanism(s) by which gravidity and pregnancy affect locomotion remains largely unexplored. Here we demonstrate that morphology, hydrodynamics and kinematics were altered during pregnancy, providing a mechanism for diminished locomotor performance in two near-term pregnant (10 days pre-parturition) bottlenose dolphins (Tursiops truncatus). Near-term pregnancy resulted in a 51±14% increase in frontal surface area, coinciding with dramatic increases in drag forces while gliding. For example, pregnant females encountered 80 N of drag at 1.7 m s–1 whereas that magnitude of drag was not encountered until speed doubled for females 18 months post-parturition. Indeed, drag coefficients based on frontal surface area were significantly greater during pregnancy (Cd,F=0.22±0.04) than at 18 months post-parturition (Cd,F=0.09±0.01). Pregnancy also induced a gait change as stroke amplitude and distance per stroke were reduced by 13 and 14%, respectively, compared with non-pregnant periods (1–24 months post-parturition). This was concomitant with a 62 and 44% reduction in mean and maximum swim speeds, respectively, during the pregnancy period. Interestingly, attack speeds of known predators of dolphins surpass maximum speeds for the pregnant dolphins in this study. Thus, pregnant dolphins may be more susceptible to predation. This study demonstrates unequivocally that changes in morphology, hydrodynamics and kinematics are associated with diminished performance during pregnancy in dolphins.

Morphological and reproductive variation among populations of the Pacific molly Poecilia butleri

In viviparous organisms, pregnant females typically experience an increase in body mass and body volume. In this study, the prediction that variation in reproductive traits among populations of viviparous organisms should be related to variation among populations in body shape was tested in the Pacific molly Poecilia butleri, a viviparous fish that inhabits western Mexico and northern Central America. Variation among 10 populations in four reproductive traits was examined: brood size, individual embryo mass, total reproductive allotment and degree of maternal provisioning of nutrients to developing embryos. Variation among these populations in body shape was also examined. Significant variation among populations was observed in both brood size and reproductive allotment but not in embryo mass or degree of maternal provisioning. Significant variation among populations was also observed in body shape. After correcting for female size, however, reproductive traits and body shape were not associated among populations. This suggests that selective pressures acting on reproduction do not necessarily affect morphology and vice versa. Several factors might contribute to this unexpected lack of association between reproductive traits and morphology.