Articles: biological-evolution.
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Mimicry--when one organism (the mimic) evolves a phenotypic resemblance to another (the model) due to selective benefits--is widely used to illustrate natural selection's power to generate adaptations. However, many putative mimics resemble their models imprecisely, and such imperfect mimicry represents a specific challenge to mimicry theory and a general one to evolutionary theory. Here, we discuss 11 nonmutually exclusive hypotheses for imperfect mimicry. ⋯ We find that the relaxed selection hypothesis has garnered the most support. However, because only a few study systems have thus far been comprehensively evaluated, the relative contributions of the various hypotheses toward explaining the evolution of imperfect mimicry remain unclear. Ultimately, clarifying why imperfect mimicry exists should provide critical insights into the limits of natural selection in producing complex adaptations.
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Facial vibrissae, or whiskers, are found in nearly all extant mammal species and are likely to have been present in early mammalian ancestors. A sub-set of modern mammals, including many rodents, move their long mystacial whiskers back and forth at high speed whilst exploring in a behaviour known as 'whisking'. It is not known whether the vibrissae of early mammals moved in this way. ⋯ We identified some differences in the extrinsic musculature which, interestingly, matched with behavioural data obtained through high-speed video recording, and indicated additional degrees of freedom for positioning the vibrissae in rats. These data show that the whisker movements of opossum and rat exploit similar underlying mechanisms. Paired with earlier results suggesting similar patterns of vibrissal movement, this strongly implies that early therian (marsupial and placental) mammals were whisking animals that actively controlled their vibrissae.
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Lower visibility of female scientists, compared to male scientists, is a potential reason for the under-representation of women among senior academic ranks. Visibility in the scientific community stems partly from presenting research as an invited speaker at organized meetings. We analysed the sex ratio of presenters at the European Society for Evolutionary Biology (ESEB) Congress 2011, where all abstract submissions were accepted for presentation. ⋯ This was lower than the baseline sex ratios of early-mid career stage scientists, but was similar to senior scientists and authors that have published in high-impact journals. High-quality science by women therefore has low exposure at international meetings, which will constrain Evolutionary Biology from reaching its full potential. We wish to highlight the wider implications of turning down invitations to speak, and encourage conference organizers to implement steps to increase acceptance rates of invited talks.
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Tipping points are recognised in many systems, including ecosystems and elements of the climate system. But can the biosphere as a whole tip and, if so, how? Past global tipping points were rare and occurred in the coupled planetary-scale dynamics of the Earth system, not in the local-scale dynamics of its weakly interacting component ecosystems. Yet, evolutionary innovations have triggered past global transformations, suggesting that tipping point theory needs to go beyond bifurcations and networks to include evolution.
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Review
Testosterone and brain-derived neurotrophic factor interactions in the avian song control system.
Interaction between steroid sex hormones and brain-derived neurotrophic factor (BDNF) is a common feature of vertebrate brain organization. The avian song control system provides an excellent model for studying such interactions in neural circuits that regulate song, a learned sensorimotor behavior that is often sexually dimorphic and restricted to reproductive contexts. Testosterone (T) and its steroid metabolites interact with BDNF during development of the song system and in adult plasticity, including the addition of newborn neurons to the pallial nucleus HVC and seasonal changes in structure and function of these circuits. ⋯ This interaction may also occur transsynpatically; T increases the synthesis of BDNF in HVC, and BDNF protein is then released on to postsynaptic cells in the robust nucleus of the arcopallium (RA) where it has trophic effects. The interaction between sex steroids and BDNF is an example of molecular exploitation, with the evolutionarily ancient steroid-receptor complex having been captured by the more recently evolved BDNF. The functional linkage of sex steroids to BDNF may be of adaptive value in regulating the trophic effects of the neurotrophin in sexually dimorphic and reproductively relevant contexts.