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71.
Dean M. Gilligan Lynn M. Woodworth Margaret E. Montgomery David A. Briscoe & Richard Frankham 《Conservation biology》1997,11(5):1235-1241
The accumulation of new deleterious mutations has been predicted to constitute a significant threat to the survival of finite sexually reproducing populations. Three measures of genetic load were made on populations of Drosophila melanogaster maintained at effective population sizes of 25, 50, 100, 250, and 500 for 45 or 50 generations and their outbred base population and a new sample from the same wild population. Genetic loads were measured as fitness differentials between inbred and non-inbred lines derived from each population under both benign ( productivity of single pairs) and competitive (competitive index) conditions. No trend of smaller populations exhibiting greater genetic loads than larger ones was observed under either benign or competitive conditions. Further, genetic loads were similar in captive and wild populations. Frequencies of deleterious and lethal alleles on chromosome II were measured by making the chromosome (approximately 40% of the genome) homozygous using a marked balancer stock. Neither deleterious nor lethal allele frequencies exhibited a relationship with population size. The accumulation of detrimental mutations does not appear to pose a significant threat to finite sexual populations with effective sizes of 25 or more over the 100–200 year time frames considered in most wildlife conservation programs. 相似文献
72.
Lynn E. Fletcher 《Behavioral ecology and sociobiology》2007,61(12):1809-1821
Group living confers both benefits and costs to the individuals involved. Benefits may include enhanced defense, thermoregulation,
and increased foraging efficiency while costs often involve competition for resources such as food, shelter, and mates. Communication
provides a medium of exchange among individuals engaged in either cooperative or competitive interactions. The functional
analysis of signals within groups therefore requires testing both cooperative and competitive functions, although the latter
is infrequently done. In this paper, I study the use of two vibrational signals in a gregarious, processionary Australian
sawfly larva, Perga affinis: tapping and contractions. Tapping involves striking the substrate with the sclerotized portion of the abdominal tail and
a contraction is a fast, whole-body twitch, which is both tactile and vibrational in its transmission. For tapping, I first
demonstrate that it is a form of communication, as tapping of one larva elicits tapping in another, and that it is transmitted
through substrate vibrations. I then test whether the signal is mostly cooperative or competitive in nature by examining it
in light of two hypotheses: (1) the Group Coordination hypothesis, stating that the signal functions to maintain group cohesiveness
and (2) the Competitive Signaling hypothesis, stating that tapping serves as a competitive assessment signal between larvae
while feeding. For contractions, I test only the group coordination hypothesis that they serve to coordinate and initiate
group movement. Results support the group coordination hypothesis for each signal. While feeding, lone larvae (without potential
competitors) were significantly more likely to tap than those in groups, and this trend continued in non-feeding situations.
Contractions regularly preceded periods of group movement during processions and were given with increasing frequency before
departure from preforaging clusters. The vibrational signals in this processionary species likely function cooperatively to
maintain group cohesiveness and coordinate movement. 相似文献
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