Learned vocal variation is associated with abrupt cryptic genetic change in a parrot species complex

<div><p>Contact zones between subspecies or closely related species offer valuable insights into speciation processes. A typical feature of such zones is the presence of clinal variation in multiple traits. The nature of these traits and the concordance among clines are expected to influence whether and how quickly speciation will proceed. Learned signals, such as vocalizations in species having vocal learning (e.g. humans, many birds, bats and cetaceans), can exhibit rapid change and may accelerate reproductive isolation between populations. Therefore, particularly strong concordance among clines in learned signals and population genetic structure may be expected, even among continuous populations in the early stages of speciation. However, empirical evidence for this pattern is often limited because differences in vocalisations between populations are driven by habitat differences or have evolved in allopatry. We tested for this pattern in a unique system where we may be able to separate effects of habitat and evolutionary history. We studied geographic variation in the vocalizations of the crimson rosella (<em>Platycercus elegans</em>) parrot species complex. Parrots are well known for their life-long vocal learning and cognitive abilities. We analysed contact calls across a <em>ca</em> 1300 km transect encompassing populations that differed in neutral genetic markers and plumage colour. We found steep clinal changes in two acoustic variables (fundamental frequency and peak frequency position). The positions of the two clines in vocal traits were concordant with a steep cline in microsatellite-based genetic variation, but were discordant with the steep clines in mtDNA, plumage and habitat. Our study provides new evidence that vocal variation, in a species with vocal learning, can coincide with areas of restricted gene flow across geographically continuous populations. Our results suggest that traits that evolve culturally can be strongly associated with reduced gene flow between populations, and therefore may promote speciation, even in the absence of other barriers.</p> </div

Comparative Analysis of Expressed Sequence Tag (EST) Libraries in the Seagrass Zostera marina Subjected to Temperature Stress

Global warming is associated with increasing stress and mortality on temperate seagrass beds, in particular during periods of high sea surface temperatures during summer months, adding to existing anthropogenic impacts, such as eutrophication and habitat destruction. We compare several expressed sequence tag (EST) in the ecologically important seagrass Zostera marina (eelgrass) to elucidate the molecular genetic basis of adaptation to environmental extremes. We compared the tentative unigene (TUG) frequencies of libraries derived from leaf and meristematic tissue from a control situation with two experimentally imposed temperature stress conditions and found that TUG composition is markedly different among these conditions (all P < 0.0001). Under heat stress, we find that 63 TUGs are differentially expressed (d.e.) at 25°C compared with lower, no-stress condition temperatures (4°C and 17°C). Approximately one-third of d.e. eelgrass genes were characteristic for the stress response of the terrestrial plant model Arabidopsis thaliana. The changes in gene expression suggest complex photosynthetic adjustments among light-harvesting complexes, reaction center subunits of photosystem I and II, and components of the dark reaction. Heat shock encoding proteins and reactive oxygen scavengers also were identified, but their overall frequency was too low to perform statistical tests. In all conditions, the most abundant transcript (3–15%) was a putative metallothionein gene with unknown function. We also find evidence that heat stress may translate to enhanced infection by protists. A total of 210 TUGs contain one or more microsatellites as potential candidates for gene-linked genetic markers. Data are publicly available in a user-friendly database at http://www.uni-muenster.de/Evolution/ebb/Services/zostera

Learned vocalizations in budgerigars (Melopsittacus undulatus): The relationship between contact calls and warble song

The budgerigar (Melopsittacus undulatus) has an extraordinarily complex, learned, vocal repertoire consisting of both the long rambling warble song of males and a number of short calls produced by both sexes. In warble, the most common elements (>30%) bear a strong resemblance to the highly frequency-modulated, learned contact calls that the birds produce as single utterances. However, aside from this apparent similarity, little else is known about the relationship between contact calls and warble call elements. Here, both types of calls were recorded from four male budgerigars. Signal analysis and psychophysical testing procedures showed that the acoustic features of these two vocalizations were acoustically different and perceived as distinctive vocalizations by birds. This suggests that warble call elements are not simple insertions of contact calls but are most likely different acoustic elements, created de novo, and used solely in warble. Results show that, like contact calls, warble call elements contain information about signaler identity. The fact that contact calls and warble call elements are acoustically and perceptually distinct suggests that they probably represent two phonological systems in the budgerigar vocal repertoire, both of which arise by production learning