Habitat and life history differences between two species of Gambusia

Abstract

Life history strategies reflect trade-offs that tend to maximize fitness, such as investment in a few large or many small offspring. We compared life histories of two temperate livebearing fishes Gambusia affinis and G. nobilis, an endangered species which is virtually unstudied. The two species persist in environments that differ widely in abiotic and biotic factors in the same local area. Gambusia affinis were typically found in habitats with high productivity and wide fluctuations in temperature, salinity and dissolved oxygen, whereas G. nobilis occurred in more stable spring-fed habitats. We collected data on life-history traits: embryo mass, brood size (number of embryos), total maternal reproductive effort, population sex ratios, and size (mass and length) distributions of adults and juveniles. There was no difference between species in reproductive effort per brood, but they differed in investment strategy. Gambusia affinis females produced large broods with small embryos, whereas G. nobilis females produced broods of fewer, larger embryos. These differences in life history strategies reflect a tradeoff between individual productivity and differential mortality rates in different environments. At our field site G. affinis persists as an annual species with relatively high growth rates and corresponding reproductive patterns, whereas G. nobilis females have a slower reproductive tempo and may live multiple years.

Maternal effects on offspring size and number in mosquitofish, Gambusia holbrooki

“…This relationship is often not detected at the population level because some mothers are “resource rich” and invest more in both traits (van Noordwijk and de Jong ). When maternal size was not accounted for our wild‐caught fish showed no relationship between offspring number and size, as reported in two other studies on Gambusia : in feral Australian populations of G. holbrooki (Trendall ) and native American populations of G. affinis (Swenton and Kodric‐Brown ). Once the largest mothers were removed from the analysis, however, offspring size and number were negatively correlated, as reported in many other poeciliid fish (Abney and Rakocinski ; Swenton and Kodric‐Brown ).…”

“…This may explain the inconsistent results reported in the literature for the relationship between maternal and offspring size among Gambusia , where there is evidence of negative (Lim et al. – unpublished data cited in the meta‐analysis digital repository), no ( Gambusia affinis : Swenton and Kodric‐Brown ), and positive correlations ( G. holbrooki : Benejam et al. ; Gambusia nobili : Swenton and Kodric‐Brown ).…”

“…), including some poeciliid fish (Benejam et al. ; Swenton and Kodric‐Brown ). Additional exploratory analyses revealed that the very largest wild G. holbrooki drove this trend.…”

“… – unpublished data cited in the meta‐analysis digital repository), no ( Gambusia affinis : Swenton and Kodric‐Brown ), and positive correlations ( G. holbrooki : Benejam et al. ; Gambusia nobili : Swenton and Kodric‐Brown ). If the relationship between maternal and offspring size is nonlinear, then it is possible to obtain each of these results by sampling a subset of the full maternal size–range.…”

Life history ofGambusia vittata(Pisces: Poeciliidae)

“…Compared to other Gambusia species of similar sizes, the brood size of G. vittata is small. Most other Gambusia species have an average brood size of 10 or more offspring, which is twice as large as G. vittata brood sizes (e.g., Gambusia puncticulata puncticulata [range of brood size across sites] = 1-70, Abney and Rakocinski, 2004; G. affinis [average number of embryos per brood] = 34.48, Swenton and Kodric-Brown, 2012; Gambusia holbrooki, = 50.8, Gkenas et al, 2012;Gambusia sexradia = 17.34, Riesch et al, 2010). An exception is Gambusia hubbsi, a species that exhibits a similar brood size compared to G. vittata (variation across low and high predation environments = 3.43-7.26, Riesch et al, 2013).…”