Timothy J. DeVoogd

Sex differences in dendritic patterns in hamster preoptic area

Sexual dimorphism is described in the dentritic field pattern of Golgi-stained neurons from the dorsomedial preoptic area of adult golden hamsters (Mesocricetus auratus). Data were obtained through a mathematical reconstruction of dentritic densities of neurons sampled from this area in males and females. Males tended to have a central concentration, while females showed an irregular dendritic density distribution with concentrations dorsolateral, ventral and medial to the area of highest dentriic density in the males. These results suggest sex differences in the afferent inputs to neurons in the dorsomedial preoptic area which may be related to functional sexual dimorphism in physiology and behavior.

Relations between Song Repertoire Size and the Volume of Brain Nuclei Related to Song: Comparative Evolutionary Analyses amongst Oscine Birds

Song and brain structure are compared amongst 41 species of oscine birds by using the method of independent evolutionary contrasts. We find a significant correlation between the relative volume of the song control centre, the high vocal centre (HVC), and the number of song types typically found in the repertoire. Relative HVC volume is not correlated with the number of different syllable types per song bout. The relative volume of a second song nucleus, area X, is not significantly correlated with either measure. Relative HVC volume is uncorrelated with relative volume of the hippocampus, a brain area involved in other forms of memory. This is the first evidence for repeated independent evolution of an association between complexity of learned song and the relative volume of one of the song control nuclei thought to be involved in song learning.

Synaptogenesis and changes in synaptic morphology related to acquisition of a new behavior

Systemic testosterone treatment induces adult female canaries to develop male-like song. This same treatment induces a doubling in size of the forebrain nucleus robustus archistriatalis (RA), known to be involved in song control, and a 51% increase in the number of synapses formed on RA neurons. In central RA, the number of synaptic vesicles per synapse increases as do several measures of synaptic size. Housing in spring-like conditions is also associated with larger synapses and more vesicles per synapse than housing in fall-like conditions. We suggest that formation of new synapses on existing neurons leading to or associated with modifications in synaptic morphology is important for acquisition of a new behavior. We also suggest that maximal behavioral and anatomical effects are associated with testosterone given under spring-like conditions.

Evolutionary changes in a song control area of the brain (HVC) are associated with evolutionary changes in song repertoire among European warblers (Sylviidae)

Determining relations between brain structure and function is a principal focus of evolutionary neurobiology. Here we investigate covariation between singing behaviour and the neuroanatomy in eight species of sylviid warblers from the closely related Acrocephalus and Locustella genera. We found a significant positive correlation between repertoire size and the volume of the higher vocal centre after controlling for variation in brain size and phylogenetic relatedness across species. This group is of particular interest, as earlier work has shown that an increase in male song complexity (as measured by syllable repertoire size) is caused by sexual selection pressure acting through female choice. Thus, in males of Acrocephalus species (which have complex songs), sexual selection appears to have led to increases in both syllable repertoire size and the relative volume of the higher vocal centre. In contrast, Locustella species have very simple songs, and repertoire size and the relative volume of the higher vocal centre remain small in males of these species. These results indicate that sexual selection may have shaped the evolution of a particular behavioural trait (song) by altering the relevant controlling area of the brain (higher vocal centre).

Variation in the volume of zebra finch song control nuclei is heritable: developmental and evolutionary implications

In many songbird species, females prefer males that sing a larger repertoire of syllables. Males with more elaborate songs have a larger high vocal centre (HVC) nucleus, the highest structure in the song production pathway. HVC size is thus a potential target of sexual selection. Here we provide evidence that the size of the HVC and other song production nuclei are heritable across individual males within a species. In contrast, we find that heritabilities of other nuclei in a song-learning pathway are lower, suggesting that variation in the sizes of these structures is more closely tied to developmental and environmental differences between individuals. We find that evolvability, a statistical measure that predicts response to selection, is higher for the HVC and its target for song production, the robustus archistriatalis (RA), than for all other brain volumes measured. This suggests that selection based on the functions of these two structures would result in rapid major shifts in their anatomy. We also show that the size of each song control nucleus is significantly correlated with the song related nuclei to which it is monosynaptically connected. Finally, we find that the volume of the telencephalon is larger in males than in females. These findings begin to join theoretical analyses of the role of female choice in the evolution of bird song to neurobiological mechanisms by which the evolutionary changes in behaviour are expressed.

Female zebra finches require early song exposure to prefer high-quality song as adults

Song learning in songbirds has been studied extensively in males but not in females. Females prefer songs previously heard, but it is not known whether opportunity for learning during the juvenile period affects the ability of females to judge song quality. We show that early exposure to adult song is required in the development of normal adult female zebra finch, Taeniopygia guttata, song preferences. Females were reared in conditions that varied in the exposure to song. As young adults, these females were tested for song preference using a two-choice speaker protocol with unfamiliar song stimuli. Females reared with adult males preferred tutored (normal-quality) song, whereas females reared without adult males were as likely to prefer untutored (abnormal-quality) song as tutored song. All three groups of females preferred conspecific to canary song but showed no preference for songs that were temporally reversed or played forward. Our results suggest that a normally reared females preference for songs with more notes and spectral complexity is learned during early exposure to adult males that produce such songs.

Greater song complexity is associated with augmented song system anatomy in zebra finches

We revisited the relationship between brain anatomy and song behavior in zebra finches. Consistent with previous studies in other songbirds, we find that differences in volume of the telencephalic song control nucleus HVc is predictive of differences in repertoire size and phrase duration in zebra finches. We extend the study of brain and behavior correlations in song birds by showing that repertoire size in zebra finches can be predicted by variance in several brain nuclei, providing the first demonstration that volumetric differences across multiple components of a neural network are predictive of song behavior.

Song, sperm quality and testes asymmetry in the sedge warbler

The phenotype-linked fertility hypothesis states that functional male fertility covaries with male phenotype and that females engage in extra-pair copulations with males with more attractive phenotypes than their partner to obtain direct fertility benefits. We tested this idea in the sedge warbler, Acrocephalus schoenobaenus, a species in which females prefer males with larger song repertoires, and in which extra-pair copulations occur. In this study paired males had larger song repertoires than unpaired males. However, we found no significant relationships between song features and any measure of sperm numbers or sperm quality. We also examined the hypothesis that directional asymmetry in testes mass covaries with the expression of secondary sexual traits, such as song features, but again found no significant eVects. However, older males tended to have larger repertoires and testes and a greater degree of directional asymmetry in testes size than young males. ? 1997 The Association for the Study of Animal Behaviour

Seasonal changes in neuron numbers in the hippocampal formation of a food-hoarding bird: the black-capped chickadee.

The volume of the hippocampal formation (HF) in black-capped chickadees (Poecile atricapillus) varies across the seasons, in parallel with the seasonal cycle in food hoarding. In this study, we estimate cell density and total cell number in the HF across seasons in both juveniles and adults. We find that the seasonal variation in volume is due to an increase in the number of small and large cells (principally neurons) in the fall. Adults also have lower neuron densities than juveniles. Both juveniles and adults show an increase in cell density in the rostral part of the HF in August and a subsequent decrease toward October. This suggests that the net cell addition to the HF may already start in August. We discuss the implications of this early start with respect to the possibility that the seasonal change in HF volume is driven by the experience of food hoarding. We also speculate on the functional significance of the addition of neurons to the HF in the fall.

Song Isolation Is Associated with Maintaining High Spine Frequencies on Zebra Finch IMAN Neurons

Male zebra finches normally learn much of their song during the second month after hatching. This is a period of rapid change throughout the brain. We studied anatomical consequences of manipulating exposure to song. We investigated neurons of lateral MAN (1MAN), a nucleus implicated in song learning (Bottjer et al., 1984), in male and female zebra finches (Taeniopygia guttata) at 55 days posthatch. Birds were raised either under normal colony conditions (social) or in colonies in which adult males were removed when the young hatched (song deprived). Brains were stained with the Golgi-Cox method. Fine morphological details of spiny 1MAN neurons were recorded with a 3D semiautomated computer system. Several features of the spiny 1MAN neurons differ between sexes. Males have neurons with larger somata, more primary dendrites and thicker dendrites, than neurons from females. These features as well as dendritic length and other branching characteristics do not differ between treatment groups. There is a large difference in dendritic spine frequencies between the social and the song-deprived groups. Social, song-experienced males have spine frequencies 41% lower than song-deprived males. In females, spine frequencies are as high as in the song-deprived males and do not differ between the song-deprived and social conditions. Developmental overproduction and subsequent pruning of neural connections have been observed in many areas of the central nervous system. We suggest that apparent pruning in 1MAN is modulated by experience: It takes place if the social experiences associated with auditory song learning have occurred. This finding is consistent with the synapse selection hypothesis of Changeux and Danchin Brain Research, 309, (1976) and with data found using an acoustic filial imprinting paradigm in the domestic chicken.