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Abstract Male-male competition is a component of Darwin’s theory of precopulatory intrasexual selection, where males compete for access to resources important for reproduction and successful males pass on traits that endow greater competitive ability to their offspring, thereby exaggerating the trait(s) over evolutionary time. Metals, such as lead (Pb) often occur in urban mangrove forests, where shore crabs reside, and being neurotoxic may cause sub-lethal effects on behaviour. In this study, we asked whether exposure to Pb influences the outcomes of male-male competition in the Semaphore crab, Heloecius cordiformis, thereby altering outcomes of intrasexual selection. Crabs were exposed to an environmentally relevant, and a behaviourally relevant, concentration of lead (i.e. Pb, 10 µg/L and 100 µg/L respectively) under laboratory conditions for 96 h and subsequently allowed to compete for burrow ownership in experimental arenas. Exposed crabs (100 µg/L) were less successful than control crabs in chela size-matched paired competitive interactions, spent less time in burrows and predominantly lost burrow ownership. Further, exposure to Pb contamination (both 10 µg/L and 100 µg/L) negated the chela size advantage in size-asymmetric competitive interactions. This contaminant-induced loss of size-related competitive advantage may result in relaxation in selection pressure on body size and smaller male carapace widths and especially male chela lengths in contaminated locations. Assessment of a range of locations in the wild found a consistent pattern of metal-associated size declines in more contaminated locations for males, but not for females.

The importance of estuarine wetlands to ecosystem services such as primary productivity and flood attenuation, as well as their function as habitat for threatened species has prompted efforts to restore tidal flows to degraded wetlands. We tracked the response of estuarine vegetation to tidal-flow reinstatement over 12 years (1995–2007) in a wetland of the Hunter estuary, Australia. This site provides important habitat for migratory shorebird species, which favour shallow tidal pools and saltmarsh over mangrove forest. Increased tidal flows following culvert removal reduced shorebird roost habitat by 17% because of mangrove encroachment on saltmarsh and shallow tidal pools. Saltmarsh occurred in areas with a spring tidal range <0.3 m, hydroperiod <1.0 and elevation >0.4 above the Australian height datum (mAHD), whereas mangrove occupied areas with spring tidal range >0.3 m, hydroperiod <0.45 and elevation <0.4 mAHD. By using these parameters, it is possible to exclude mangrove from saltmarsh areas and to establish saltmarsh at lower elevations in the tidal frame than would occur under natural conditions, effectively expanding saltmarsh area. These measures can be useful where landward migration of estuarine communities is restricted by infrastructure; however, they should not be considered a substitute for conservation of remnant saltmarsh or establishment of landward buffer zones. [ABSTRACT FROM AUTHOR]

We report the findings of a phylogenetic comparative analysis examining patterns and frequency of occurrence of same-sex courtship and mounting behavior in birds. Our analysis has shown associations between same-sex sexual behavior and both mating system and degree of precociousness at hatching. The patterns of expression and frequency of occurrence of same-sex sexual behavior differed markedly for males and females. Patterns of same-sex sexual expression reflected the competitive sexes that actively solicit sexual interactions in heterosexual encounters. Male–male (MM) sexual behavior occurred across all mating systems, but MM mounting was significantly more prevalent in those species with facultative polygamy. The frequency of MM sexual behavior increased with degree of polygamy. Female–female (FF) sexual behavior (especially courtship) occurred most frequently in socially monogamous species and rarely occurred in species that display obligate polygamy (predominantly polygynous species). Both expression and frequency of FF sexual behavior was strongly related to the precocial state of development at hatching. FF sexual behavior is more likely to occur in species in which monogamy occurs together with the production of precocial offspring; that is, in monogamous species that are exceptions to the more common altricial mode of development. We suggest that requirement of biparental care in monogamous species may influence the greater expression of FF sexual behavior and longer term associations. Both spatial and behavioral dispersion of females and engagement in uniparental care may be important in explaining the lower incidence of FF sexual behavior in polygynous species. Social contexts where males congregate at communal leks or display areas may influence the greater expression and frequency of MM sexual behavior in polygynous species. [ABSTRACT FROM AUTHOR]