The function and speciation potential of short- and long-range song in a songbird, the dark-eyed junco (Junco hyemalis)

Divergence in mating signals can promote diversification and reproductive isolation through assortative mating.  In many taxa, acoustic signals are essential for mate attraction and choice and are known to diverge in response to both sexual selection and selection for efficient sound transmission. Previous research on song divergence and mate choice in birds has focused exclusively on high amplitude, “long-range songs” (LRS) important in territoriality and mate attraction. However, many species also produce low amplitude, “short-range songs” (SRS) associated with male-female interactions during courtship and male-male aggressive interactions, the function of which is poorly understood. My dissertation research seeks to determine the function of SRS and the role of SRS in assortative mating and promoting reproductive isolation within the Junco genus.

Recent molecular evidence indicates the Dark-eyed Junco (Junco hyemalis) radiated into five distinct subspecies as recently as 5,000 years ago. During this radiation, each subspecies developed a unique range, plumage, and morphology, making the junco an informative case of rapid divergence and potentially incipient speciation. Dark-eyed junco song consists of distinct LRS and SRS types that differ substantially in length, complexity, and frequency bandwidth, all of which are greater in SRS (Figure 1). Junco SRS can be further divided into two classes based on differences in tempo. Slow tempo SRS (slow SRS) is produced by male juncos and directed towards females during courtship. Fast tempo SRS (fast SRS) is also sung by males and can be directed towards both males and females.

Male juncos presented with a territorial intrusion of LRS or SRS respond more aggressively to SRS. This aggressive response is even stronger when a male's mate is fertile and his risk of being cuckolded by a rival male is at its highest, suggesting that SRS serves a function in courtship (Reichard et al., 201X). If SRS is functioning in courtship and playing an important role in mate choice, then divergence in SRS has the potential to act as an isolating mechanism. However, in the junco and most passerines, little is known about within and/or between subspecies variation in SRS or its role in species recognition and assortative mating.

Figure 1. Representative spectrograms of Dark-eyed Junco long-range song (TOP), slow short-range song (MIDDLE), and fast short-range song (BOTTOM).

CLICK HERE TO PLAY THE LRS SAMPLE

CLICK HERE TO PLAY THE SLOW SRS SAMPLE

CLICK HERE TO PLAY THE FAST SRS SAMPLE

PUBLICATIONS

*Rosvall, K.A., *Reichard, D.G, Ferguson, S.M., Whittaker, D.J., and Ketterson, E.D. 2012. Robust behavioral effects of song playback in the absence of testosterone or corticosterone release. Hormones and Behavior 62(4): 418-425. *denotes equal author contribution

Reichard, D.G., Rice, R.J., Vanderbilt, C.C., and Ketterson, E.D. 2011. Deciphering information encoded in birdsong: male songbirds with fertile mates respond most strongly to complex, low-amplitude songs used in courtship. American Naturalist 178(4): 478-487.

PRESENTED PAPERS

Reichard, D.G., Rice, R.J., Vanderbilt, C.C., and Ketterson, E.D. Secret serenades: complex, low-amplitude song elicits an elevated response in a male songbird. Joint Meeting of the Animal Behavior Society and the International Ethological Congress, Bloomington, Indiana. July 2011. (Oral Presentation)

Vanderbilt, C.C., Reichard, D.G., and Ketterson, E.D. Differences in structure and tempo of low-amplitude song affect male aggressive response in Dark-eyed Juncos. American Ornithologists' Union Conference, Jacksonville, Florida. July 2011. (Poster)

Reichard, D.G., Rice, R.J., and Ketterson, E.D. The function of complex low amplitude vocalizations in Dark-eyed Juncos: male response to     short- and long-range song. American Ornithologists' Union Conference, San Diego, CA, February 2010 (Oral Presentation)

Reichard, D.G. and Ketterson, E.D. Decoding an enigmatic signal: short-range song in Dark-eyed Juncos (Junco hyemalis). American Ornithologists' Union Conference, Philadelphia, PA, August 2009 (Poster)

Reichard, D.G. and Ketterson, E.D. Geographic variation in Dark-eyed Junco song: potential for reproductive isolation? American Ornithologists' Union Conference, Portland , OR, August 2008. (Oral Presentation)