Search

Runoff containing road salt (sodium chloride, NaCl) causes the salinization of inland freshwaters, with potentially severe impacts on aquatic species. We performed a mesocosm experiment to test the effects of salinization on plankton community structure in an oligotrophic mountain lake with a limited history of elevated salt concentrations. We exposed plankton communities to a gradient of 30 salt concentrations ranging from 1 to 2900 Cl− mg L−1 for 6 weeks. Adding salt increased zooplankton biomass at concentrations < 500 mg Cl− L−1 while reducing phytoplankton biomass. Zooplankton biomass declined precipitously at higher concentrations, with phytoplankton biomass showing a mirror image increase. The initial increase in zooplankton biomass with salt addition suggests that zooplankton are salt-limited at low ionic concentrations. Additionally, the inverse response of zooplankton and phytoplankton suggests that salinity mainly affects phytoplankton biomass via changes in top-down regulation by grazers.

Metabolism is a fundamental attribute of all organisms that influences how species affect and are affected by their natural environment. Differences between sexes in ectothermic species may substantially alter metabolic scaling patterns, particularly in viviparous or live-bearing species where females must support their basal metabolic costs and that of their embryos. Indeed, if pregnancy is associated with marked increases in metabolic demand and alters scaling patterns between sexes, this could in turn interact with natural sex ratio variation in nature to affect population-level energy demand. Here, we aimed to understand how sex and pregnancy influence metabolic scaling and how differences between sexes affect energy demand in Gambusia affinis (Western mosquitofish). Using the same method, we measured routine metabolic rate in the field on reproductively active fish and in the laboratory on virgin fish. Our data suggest that changes in energy expenditure related to pregnancy may lead to steeper scaling coefficients in females (b  = 0.750) compared to males (b  = 0.595). In contrast, virgin females and males had similar scaling coefficients, suggesting negligible sex differences in metabolic costs in reproductively inactive fish. Further, our data suggest that incorporating sex differences in allometric scaling may alter population-level energy demand by as much as 20–28%, with the most pronounced changes apparent in male-biased populations due to the lower scaling coefficient of males. Overall, our data suggest that differences in energy investment in reproduction between sexes driven by pregnancy may alter allometric scaling and population-level energy demand. [ABSTRACT FROM AUTHOR]

The most widespread and numerous inland fish in the world is likely the mosquitofish (Gambusia affinis and G. holbrooki, Poeciliidae). Much has been written about the basic biology, the current distribution and the negative impacts of non‐native populations of mosquitofish. Here, we instead review the relationship of humanity with mosquitofish. First, we review the early literature on the species and aim to resolve its path towards becoming the globally dominant fish for biological control of mosquitoes. We identify the initial advocates of mosquitofish use, we examine the reasons behind their advocacy, and we document the spread of their viewpoints into and from the globally foundational mosquito control texts. Second, we identify the people and institutions that facilitated early international translocations of mosquitofish, including, among others, David Starr Jordan, the Rockefeller Foundation and the International Red Cross. Third, we discuss the reduction in mosquitofish translocation and use during and after WWII, initially stemming from the discovery and use of other methods, like DDT and later from a recognition of the negative ecological consequences of non‐native mosquitofish populations. Fourth, we propose that the future utility of mosquitofish is largely in its value as a model study organism. We provide an overview of the contributions mosquitofish have made to some major fields in biology. Finally, we suggest that the value of mosquitofish as a model system should increase into the future, behind a momentum of research advances, and as human‐mediated range expansion will permit access to mosquitofish by yet greater numbers of biologists worldwide. [ABSTRACT FROM AUTHOR]