Skull and body size usually don't change anymore in fully-grown animals. Red-toothed shrews (Sorex spp.) are a notable exception: they shrink in anticipation of the winter and regrow in preparation for reproduction. This process affects the brain, several other major organs, bones and also the cognitive abilities. The phenomenon is also found in weasels, which share many life history traits, especially an exceedingly high metabolism. The study is important for our understanding of evolution, and has profound implications for medical research.
Species-specific seasonal changes of bird song, that are caused by sex hormones, can be a consequence of distinct gene expression patterns induced in the song control system. In songbirds, different sex hormone activities are based on divergent genomic regulatory mechanisms. However, neuronal wiring of the songbird as well as mammalian brain is modified by sex hormones via to some extent comparable cellular processes.
Anisogamy leads to females being expected to be the choosier sex. However, when females cheat on their social partners, they seek males as mates that are older than their social partner but with whom they produce offspring of lower fitness. This is what a team around researchers of the MPI for Ornithology found in house sparrows. Also, old mothers produced daughters of low fitness compared to young mothers. These findings are important, as this patterns has been found to a limit also in humans. Thus, with increasing age of reproduction we may pass on the costs of this to the next generation.
Environmental factors can have a large impact on behaviour and the underlying physiology. For example, island canaries advance the onset of breeding in response to growing plants. In zebra finches both song and the song control regions in the brain show low heritability but are highly sensitive to changes of the environment. In contrast, brain size largely depends on the interaction between genes and the environment. In this way additive genetic variation is maintained. These results emphasize the major importance of environmental factors for vocal learning and neural development in songbirds.
Hormones, as parts of complex regulatory systems, mediate environmental adjustments of organisms. Can hormonal systems change fast enough to keep up with rapid changes in the environment? In birds, concentrations of the hormone corticosterone are related to evolved differences in reproductive investment. Even within a bird species corticosterone patterns predict the reproductive success of individuals. Future studies will determine selection pressures, heritabilities and rate of evolutionary changes in hormones.
It is well established that urban areas have been successfully colonized by animals. Less is known about the extent to which urbanization causes ecological and micro-evolutionary changes in animals thriving in urban areas. Studies at the MPIO in Radolfzell elucidate that city life causes changes in behavior and underlying physiological mechanisms and that micro-evolutionary effects may play an important role. Current studies using newest radiotelemetry and micrologger technique aim to discover the impact of artificial city light at night on the daily and seasonal organization of urban animals.