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A repeated pattern of background colour matching in animals is an indication that pigmentation may be cryptic. Here, we examine the relationship between pigmentation of the freshwater isopod Asellus aquaticus and background darkness in 29 lakes, wetlands and ponds in Southern Sweden. The results show that Asellus pigmentation was correlated with substrate darkness across all localities. In seven localities, in which two contrasting substrate types were noted, Asellus populations were differentiated with respect to pigmentation. These findings thus provide phenomenological support for cryptic pigmentation in Asellus. Pigmentation generally increased with body size, but the relationship between pigmentation and size differed among localities, possibly as a result of differences in correlational selection on pigmentation and size. Selection thus appears to have resulted in local differentiation over a small spatial scale, even within lakes and wetlands. This differentiation is a likely cause behind elevated phenotype variation noted in localities with two substrate types, suggesting that habitat heterogeneity promotes genetic diversity.

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The role of sperm number and quality in male competitiveness was investigated using in vitro fertilization experiments with bluegill (Lepomis macrochirus). Bluegill males use one of three mating tactics: ‘sneakers’, which streak spawn; ‘satellites’, which mimic females; and ‘parentals’, which are territorial. The in vitro experiments mimicked natural spawning by incorporating these males’ mean proximity to eggs and timing of sperm release. Using a maximum‐likelihood algorithm, raffle equations were fit to paternity data, which revealed a strong effect of sperm number on male competitiveness. There was no difference in sperm flagellum length, curvilinear swim speed or path linearity among the three male mating types, and these traits did not explain any additional variation in male competitiveness. It was estimated that, given closer proximity to eggs, satellites need release only 0.34 times as many sperm as parentals to obtain equal paternity. Despite being farther from the eggs and releasing sperm about half a second after parentals, sneakers need only release 0.58 times as many sperm as parentals to obtain equal paternity. Thus, the increased competitiveness of sneakers’ sperm must come from a component of sperm quality other than speed or length.

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Summary1. Increases in longevity from dietary restriction (DR) have been linked to the evolution of physiological strategies for maintaining lifetime reproductive output despite periods of nutritional deficiency. If this is the case, then reproductive life history and mating status should determine whether or not dietary restriction increases longevity. 2. We investigate the effects of DR and mating status (mated or unmated) on longevity and lifetime reproductive output and explore mechanisms underlying these patterns by measuring resting energetic rates and changes in mass over time. We study iteroparous female Australian redback spiders (Latrodectus hasselti), which are known to tolerate periods of starvation (ecologically relevant DR) in nature. . Most strikingly, mated females (whether DR or not) had higher longevity than unmated females. 4. Mated females rapidly decreased their resting energetic rates and stopped egg production under DR. Once feeding returned to normal, resting energetic rates of mated females increased immediately, egg sac production continued and there was no net decrease in lifetime reproductive output relative to mated females without DR. 5. This shows DR increases longevity for mated females, but there is a longevity cost of remaining unmated, which may arise because unmated females (regardless of diet) maintained high energetic rates. This may be an evolved pattern of physiological support for reproductive readiness which exerts a fitness cost when mating is delayed. Taken together, these results suggest positive effects of DR on longevity critically depend on reproductive life history (iteroparity or semelparity) and individual mating status.

Irresistible: Amino acid derivatives are very rarely used as pheromones by arthropods. The widow spider Latrodectus hasselti (see picture) uses a unique compound (see formula) to lure its males. The molecular configuration plays an important role in this unique chemical communication system.