Date of Award

5-1-1979

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Sympatric populations of greater prairie chickens (Tympanuchus cupido) and sharp-tailed grouse (Pedioecetes phasianel lus) were studied between 1975 and 1978 in northwestern Minnesota for the pur poses of identifying and determining the strength of reproductive isolating mechanisms between them. Major emphasis was placed on ethological mechanisms but other factors were also examined.

Approximately a fifth of the sharptail’s distribution overlaps half of the prairie chicken’s within North America. Within the zone of sympatry, prairie chicken populations are in small patches and may be liable to hybrid swarming, particularly with changes in land-use practices. The rate cf hybridization is around 1% but may be much greater in specific areas.

Within the Minnesota study area, hybridization increased from 1-3.7% as the ratio between numbers of prairie chickens and sharptails increased. Habitat preferences and seasonal and daily patterns of activity were sufficiently similar between species to allow complete intermixing. Breeding experiments conducted in captivity showed that hybrids and backcrosses were interfertile. Thus, non-communica- tory mechanisms were weak or non-existent.

Agonistic displays, including forward displays, face offs and stand offs were similar between SDecies and probably facilitated spacing as all males held interspecifically exclusive territories on mixed displa.- grounds. Most epigamic behaviors such as booming displays, whoops, dancing and chi Iks were polyvalent and had many species-specific characteristics. Discriminant analysis and canonical correlation analysis were used to show that whoops and chi Iks, which were mostly epigamic, were most different between species; whines, which were polyvalent, were more similar; and cackles, the most aggressive of the 3 sets of vocalizations, were most similar between species. Interrelationships of homologous displays, as determined by cluster analyses, and by temporal occurrence of common displays, were not sufficiently different to be effective isolating mechanisms. Displays of hybrids were intermediate in form between both parental species and may have repulsed females.

Intraspecific playback experiments of vocalizations showed that prairie chicken booms, whoops and composite calls (consisting of a segment of a recording made while a prairie chicken hen visited a display ground) had agonistic functions. Prairie chicken whines also elicited significant responses but this call appeared to serve as an alarm. Sharptail males responded aggressively to gobbles, coos, cackles and alert. The functions of dancing in intermale communication were unclear.

Analyses of activity rates showed that males of both species responded .tore vigorously to live and taxidermist mounts of conspe- cific hens than to heterospecifics. Male prairie chickens, unlike sharptails, frequently courted live heterospecific females, even if doing so led to fights. Prairie chicken males reacted aggressively to sharptail coos, gobbles, cork notes and composite sounds while sharp-tails only responded to prairie chicken cackles. Increased selectivity of sharptails for nonspecific stimuli may be due to greater historical contact with confamilials and a resulting channelization of reproduc tive and aggressive energies to meet intraspecific competition.

During experiments conducted in captivity, females of both species strongly preferred conspecific territories and males despite being raised in mixed-species groups from hatching. FI hybrid and backcross females were more ambiguous but may have preferred sharp- tail males. Precise factors determining mate choice by females were unidentified but appeared to relate to possession of a territory and to behaviors of males.

Of the mechanisms studied, behavior, particularly communication, seemed to be most important in maintaining species integrity between greater prairie chickens and sharp-tailed grouse. Based on similari ties in the displays of the two species and cn apparent fertility of hybrids, both grouse should be considered congeneric under Tympanuchus.

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