Articles: biological-evolution.
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Drug Alcohol Depend · Jun 2012
ReviewCommon liability to addiction and "gateway hypothesis": theoretical, empirical and evolutionary perspective.
Two competing concepts address the development of involvement with psychoactive substances: the "gateway hypothesis" (GH) and common liability to addiction (CLA). ⋯ Whereas the "gateway" hypothesis does not specify mechanistic connections between "stages", and does not extend to the risks for addictions, the concept of common liability to addictions incorporates sequencing of drug use initiation as well as extends to related addictions and their severity, provides a parsimonious explanation of substance use and addiction co-occurrence, and establishes a theoretical and empirical foundation to research in etiology, quantitative risk and severity measurement, as well as targeted non-drug-specific prevention and early intervention.
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Gen. Comp. Endocrinol. · May 2012
ReviewHormones, life-history, and phenotypic variation: opportunities in evolutionary avian endocrinology.
Life-histories provide a powerful, conceptual framework for integration of endocrinology, evolutionary biology and ecology. This has been a commonly articulated statement but here I show, in the context of avian reproduction, that true integration of ultimate and proximate approaches has been slow. ⋯ Endocrine systems provide strong candidate mechanisms for regulation of phenotypic variation in single traits, and two endocrine concepts capture the essence of life-history trade-offs: (a) hormonal 'pleiotropy', when single hormones have both positive and negative effects on multiple physiological systems and (b) hormonal conflict between regulatory systems required for different but over-lapping or linked life-history stages. I illustrate these ideas with examples of reproductive anemia, migration-reproduction overlap, and molt-breeding overlap, to highlight some of the tremendous opportunities that exist for comparative endocrinologists to contribute to mechanistic studies of avian reproduction in an evolutionary context.
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Am. J. Phys. Anthropol. · May 2012
Placement of the diaphragmatic vertebra in catarrhines: implications for the evolution of dorsostability in hominoids and bipedalism in hominins.
A fundamental adaptation to orthograde posture and locomotion amongst living hominoid primates is a numerically reduced lumbar column, which acts to stiffen the lower back and reduce injuries to the intervertebral discs. A related and functionally complementary strategy of spinal stability is a caudal position of the diaphragmatic vertebra relative to the primitive condition found in nonhominoid primates and most other mammals. The diaphragmatic vertebra marks the transition in vertebral articular facet (zygapophysis) orientation, which either resists (prediaphragmatic) or allows (postdiaphragmatic) trunk movement in the sagittal plane (i.e., flexion and extension). ⋯ I show that while hominoids are characterized by modal common placement of diaphragmatic and last rib-bearing vertebrae in general, interspecific differences in intraspecific patterns of variation exist. In particular, humans and chimpanzees show nearly identical patterns of diaphragmatic placement. A scenario of hominin evolution is proposed in which early hominins evolved cranial displacement from the ancestral hominid condition of common placement to achieve effective lumbar lordosis during the evolution of bipedal locomotion.
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The evolution of floral traits may be shaped by a community of floral visitors that affect plant fitness, including pollinators and floral antagonists. The role of nectar in attracting pollinators has been extensively studied, but its effects on floral antagonists are less understood. Furthermore, the composition of non-sugar nectar components, such as secondary compounds, may affect plant reproduction via changes in both pollinator and floral antagonist behavior. ⋯ However, this effect varied across sites such that the sites that were most pollen-limited were also the sites where nectar alkaloids had the least effect on pollen receipt, resulting in no significant effect of nectar alkaloids on fruit set. Finally, high nectar gelsemine significantly reduced seed weight; however, this effect was mediated by a mechanism other than pollen limitation. Taken together, our work suggests that nectar alkaloids are more costly than beneficial in our system, and that relatively small-scale spatial variation in trait effects and interactions could determine the selective impacts of traits such as nectar composition.