Experimental studies on water strider mating dynamics: spatial variation in density and sex ratio

James J. Krupa, Andrew Sih

Research output: Contribution to journalArticlepeer-review

122 Scopus citations

Abstract

We used field surveys, field experiments and experiments in artificial pools to study the effects of variation in sex ratio and density on mating dynamics of a stream water strider, Aquarius remigis. Our field survey documented the existence of "hot spots", sites of higher than average total gerrid density, a male-biased sex ratio, and higher than average female mating activity. Female gerrids frequently changed sites, usually moving upstream, perhaps to spread their eggs among many sites. Male gerrids showed two movement strategies: some males frequently changed sites, while other males were stationary at hot spots. Surprisingly, smaller males tended to be stationary at hot spots. A field manipulation of the availability of refuges for females to avoid harassment by males supported the notion that males prefer hot spots because they are sites where a scarcity of refuge for females makes it relatively easy for males to intercept females. Experiments in plastic pools compared sites with 20 males: 5 females (simulating hot spots) to pools with 5 males: 5 females. The rate of male harassment of females was higher in 20:5 pools as compared to 5:5 pools. In response to increased male harassment, females reduced their activity on the water and increased their time spent out of the water and thus unable to forage. Males showed a large male mating advantage (LMMA) in 5:5 pools, but, surprisingly, not in 20: 5 pools. This pattern can explain the field observation that small males prefer hot spots. A behavioral mechanism that can explain the LMMA is as follows. Mating occurs when males overcome female resistance. Larger males have a mating advantage over smaller males if females resist heavily. Increased harassment (e.g., in 20:5 pools as compared to 5:5 pools) might result in reduced female resistance to males and thus a reduced LMMA. Females also showed some non-random mating by size that might reflect an interplay between male preference for large females and the avoidance of males by large females.

Original languageEnglish
Pages (from-to)107-120
Number of pages14
JournalBehavioral Ecology and Sociobiology
Volume33
Issue number2
DOIs
StatePublished - Aug 1993

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology

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