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For example, if a male detects a courting group with one male and one female in a population with an OSR of four males to every female, then all else being equal, the male should benefit from approaching this group because he is apt to encounter more competitive mating prospects if he continues to search for mates (assuming that local OSRs are normally distributed around the population OSR).
In addition to spatial variation in local OSRs, population OSRs often vary temporally (Kvarnemo and Ahnesjö, 1996), further complicating the decision to approach a courting group.
Finally, we attempted to characterize the chemical cue released from males that provides information on local OSR.
This first field experiment was designed (1) to assess whether male newts prefer less competitive reproductive opportunities, and (2) to determine how male-male competition affects the likelihood of amplexus, the act of a male clasping the neck of a female with his hindlimbs that is typically a prerequisite to mating in nature (Massey, 1988; Verrell, 1982, 1984).
Groups of four males and individual females were housed separately in plastic containers filled with dechlorinated tap water, were maintained in a controlled environmental chamber at 18°C on a 14-h light/10-h dark cycle, and were fed a liberal diet of chopped earthworms and freeze-dried bloodworms daily.
The unique dorsal spot pattern of each newt was recorded to facilitate identification during trials (Gill, 1978).
We addressed these gaps in the literature by using the mating system of the eastern red-spotted newt, .In fact, temporal variation in population OSRs has been associated with shifts in competition for mates (Ahnesjö, 1995; Grant et al., 2000) and reversed sex roles in a variety of species (Gwynne and Simmons, 1990; Simmons, 1992; Vincent et al., 1994).In theory, as the population OSR varies temporally, so too should responses to local OSRs because the probability of finding less competitive mating prospects should parallel changes in the OSR of the population.We used amplexus to estimate mating probability because we wanted to stop each trial before spermatophore deposition so that the OSR of our experimental animals remained relatively constant across trials.Forty-four adult male and 11 adult female red-spotted newts were collected from a private pond in Chenango County, New York, in late May 2000.