Nancy Tyler Burley - US grants

NON-TECHNICAL SUMMARY

The Role of Choice in Avian Speciation

A question of central interest to scientists studying the process of evolution is how the formation of new species ("speciation") occurs. Common mechanisms of speciation involve physical isolation of populations for long periods of time: when sufficiently isolated such that virtually no migration occurs between populations, populations regularly diverge in their traits. If isolation continues long enough, the result is speciation. Even occasional migration between populations, however, leads to gene exchange that prevents genetic divergence of populations from occurring, at least when the consequence of mi.-ration is joint reproduction of individuals derived from different populations. Thus, the tendency of organisms to accept as mates those individuals born in different populations should affect the probability and rate of speciation. For organisms with good powers of dispersal, physical isolation between populations may occur rarely, and mate choice for members of one's natal population could have an important role in speciation processes.

This study experimentally investigates the occurrence and significance of mate preferences for natal population in two populations of longtailed finches. The longtailed finch is a small songbird native to nor-them Australia; although it is a strong flier, natural populations occurring at short distances from one another are highly distinctive. Preliminary work has established that birds from one population refuse to mate with birds from a different population. Additional work will determine the causes and functions of this preference for natal population. Research will include investigation of the cues birds use to recognize birds from their own population; how early life experiences may modify a bird's perception of what constitutes "its own" population; and the role of preferences for associating with kin in these population preferences.

Results of these experiments will be relevant to several broad areas of contemporary scientific exploration in biology, including population biology, evolution, ecology, and animal behavior. Results may be useful in furthering our understanding of captive breeding of wild animals and management of threatened species.

Behavioral Functions of Vocal Imitation in Parrots

PI: Georg F. Striedter
co-PI: Nancy T. Burley

Why do some animals imitate complex sounds? This question has most frequently been addressed in songbirds, which learn their songs primarily to defend a territory and/or attract a mate. These explanations may not hold for the parrots, however, because parrots have evolved their remarkable imitative abilities independently of the songbirds. So, why do parrots imitate sounds? Recent data from the Striedter laboratory suggest that parrot vocal learning plays a role in pairbond formation. Specifically, when male and female budgerigars are placed in pairs, the males consistently imitate the contact calls of the females with whom they are paired, while the females retain their original calls. This sexual asymmetry in imitative behavior suggests that males imitate females in order to influence female mate choice. If this hypothesis is correct, then three predictions should hold: 1) Sexual selection should have led to an asymmetry in the vocal learning abilities of male and female budgerigars. This hypothesis will be tested by comparing how quickly all-male and all-female groups of budgerigars develop shared contact calls. If males are "better" at vocal learning, then vocal convergence should occur more quickly among males than among females. 2) Males should preferentially imitate females whom they are courting. This hypothesis will be tested by determining whether the time it takes for a male to learn a female's call is inversely correlated with his interest in this female, as measured by the frequency of other, well-known courtship behaviors. The female's attractiveness will be manipulated by painting her cere, which is brown in mature females but pale blue in immature females. 3) Female budgerigars should associate preferentially with males that have learned to imitate them. This hypothesis will be tested by determining whether females give more courtship displays towards unfamiliar males that already know their call (because they were tutored by another female that shares the test female's call) than towards males that do not yet know the test female's call. In a complementary experiment, some male budgerigars will be rendered imitation-impaired by selectively severing the connection between their auditory and vocal motor systems. The proposed experiments could significantly impact the field of "sexual selection" and "female choice" because most prior studies focused on female choice for overt physical traits - not learning ability. The proposed experiments also pave the way for a more mechanistic analysis of why male budgerigars imitate female calls.