There is relatively little known about nitrate toxicity in aquatic invertebrates, especially sublethal effects of elevated nitrate. We exposed the amphipod Gammarus pseudolimnaeus to elevated nitrate concentrations (up to 128 mg NO(3)-N/L) in a laboratory experiment and measured mortality, growth rates, egestion rates, molting, and C:N ratio. Nitrate concentration did not affect mortality, egestion rate, molting, and C:N ratio. Amphipod growth decreased slightly with increasing nitrate concentration based on the results of a linear regression, but a one-way ANOVA suggested that mean growth rates were not different among nitrate treatments. We suggest that additional research is needed on the sublethal effects of elevated nitrate concentration on aquatic invertebrates, particularly for those taxa that have demonstrated sensitivity to other chemical stressors.
In the field of emotion regulation studies, cognitive reappraisal has been established as the preferred strategy for coping with painful negative feelings. For some, however, asking them to think more about an already distressing situation can be quite literally "like pulling teeth." Indeed, many people voluntarily cause themselves physical pain during upsetting situations (e.g., getting a deep tissue massage after a stressful week or hitting a punching bag when angry); however, there is currently little empirical evidence of the relative effectiveness of such behaviors. The present study tested two primary hypotheses: (a) some people will choose to inflict pain to regulate negative emotional states; and (b) pain provides effective short-term relief from negative emotion. The findings from these two studies demonstrate that, given the opportunity, participants will choose to use physical pain in addition to other strategies, like reappraisal or distraction, to cope with various sources of negative emotion. We further show that physical sensation in general, and pain in particular, are equally effective in coping with negative emotion. These results suggest a reconsideration of the dominance of cognitively based emotion regulation. We discuss the implication that benign physical pain may be a broadly effective and underrecognized coping strategy.
Gynogenesis is a peculiar mode of clonal reproduction in which eggs need to be pseudo-fertilized by sperm, but the male genes are not passed on to the offspring. One mating system in which gynogenesis is found involves a unisexual hybrid, the Amazon molly (Poecilia formosa), which typically uses males of its two parental species as sperm donors. Most gynogenetic lineages do not sexually parasitize males that were not involved in their hybrid origin and although some gynogens have the ability to utilize males from additional species, they rarely occur in sympatry with more than one sperm host. A few populations of the Amazon molly, however, do occur syntopically with more than one host species, raising the question of whether specific preferences have evolved in P. formosa and whether Amazon mollies can now act like Red Queens, driving the evolution of discrimination abilities in the host species. Near Ciudad Mante, Mexico, the critically endangered Tamesí molly (P. latipunctata) occurs in exclusive sympatry with Amazon mollies and one of P. formosa's parental species, the Atlantic molly (P. mexicana). In this study we tested the initial and post-exposure preference of allopatric and sympatric P. formosa (with regards to P. latipunctata) between P. latipunctata and P. mexicana males. We predicted that P. formosa should favour P. mexicana because this is a parental species to P. formosa and the asexual shares half of the P. mexicana genome. Contrary to our predictions, we found no significant differences between preference scores in allopatric and sympatric populations of P. formosa in initial or postexposure trials. Our findings may indicate that males of both species are perceived as equally effective in triggering embryogenesis by P. formosa. This study, along with limited previous work in the system, calls to attention the exploration of the adaptive ability of gynogenetic species relationships, and their implications for the long-term persistence of not only asexual lineages, but also the parasitized sexual species.
During ecological speciation, diverging taxa have the potential to remain in close spatial proximity (i.e., sympatry or micro-allopatry) theoretically allowing for continued contact and gene flow. In a system where incipient speciation of populations of the Atlantic molly (Poecilia mexicana) appears to be driven by abiotic factors, we investigated whether one of these factors, hydrogen sulphide (H 2 S) toxicity, also constitutes an effective barrier to slow migration within and between habitats. We addressed this experimentally by translocating individuals from high toxicity to lower toxicity within a toxic cave and by translocating individuals from the toxic cave to a nontoxic surface habitat. Using a stepwise-backwards Cox regression, we found that overall mortality was low, but statistically significant mortality occurred when individuals were transferred from higher toxicity to lower toxicity. In addition, only males were negatively affected by being transferred from low levels of toxicity to nontoxic, surface waters. This indicates that in addition to abiotic factors, other mechanisms, like predation and sexual selection, must be important in maintaining population separation.
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