It is generally believed that predation pressure may drive the evolution of long spines, a robust pelvic girdle, and a deep body in sticklebacks (Pisces: Gasterosteidae). However, the lack of such traits in environments under intense predation pressure suggests that there may be a limit to which these apparently defensive structures benefit sticklebacks. In some environments, well-developed defensive structures may not increase stickleback survival, but may actually reduce fitness if there is a cost associated with them. This paper focuses on a trade-off between defensive morphology and escape-response performance in the brook stickleback (Culaea inconstans). Our study of four populations of brook stickleback reveals that the population with the largest pelvic girdles and deepest bodies has a poorly developed escape response (i.e., small displacement, low maximum velocity, and low acceleration), while the population with the smallest pelvic girdles and shallowest bodies has a highly developed escape response. The two populations with intermediate defensive structures are intermediate in escape-response performance. Consideration of predation regimes in different environments may help us understand selection pressures that favor heavily versus poorly armored stickleback morphs.

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The northern redbelly dace (Chrosomus eos) and the finescale dace (C. neogaeus) have hybridized to produce an all-female, asexual hybrid (C. eos-neogaeus) that reproduces by sperm-limited parthenogenesis (gynogenesis). However, in this system, gynogenesis is not 100 % efficient; triploid females are occasionally formed which reproduce as sexuals, producing nuclear males and females of the paternal species (generally C. eos). Thus, the asexual lineage continually produces occasional males that can serve as a sperm source. Because (almost) all hybrid offspring are females, the hybrid population has the potential to grow more quickly and even outcompete the sexuals, thus eliminating their own sperm source. The current research uses behavioral testing, ovarian analyses, and modeling to examine three hypotheses for the maintenance of the sexual/asexual complex: male discrimination against hybrid females, fecundity differences between sexual and asexual females, and production of nuclear male sexuals from the asexual lineage. Results suggest that males do not discriminate against asexual females, and that both sexual and asexual females have similar fecundities, eliminating these hypotheses as potential coexistence mechanisms. However, computer simulations of population growth support the hypothesis that occasional triploidy within the hybrid population supplies enough breeding males to maintain the sexual/asexual complex.

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The presence and/or absence of certain bacteria suggested disease-specific ecological or micro-environmental pressures driving or excluding certain organisms in Crohn's disease. The data suggest that several of the dysbiotic conditions previously reported for Crohn's disease are not unique but common to general dysbiosis. The examination of multiple intestinal sites in advanced disease may provide a spectrum of disease from early onset at the resection margin to active disease at the disease margin and late-stage fibrostenotic disease at the centre of the lesion, and a unique etiopathogenic view of Crohn's disease.

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