Elsevier

Animal Behaviour

Volume 109, November 2015, Pages 23-31
Animal Behaviour

Experimental limitation of oviposition sites affects the mating system of an arachnid with resource defence polygyny

https://doi.org/10.1016/j.anbehav.2015.08.007Get rights and content

Highlights

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    We manipulated natural oviposition site availability of a male-dimorphic harvestman species.

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    Females and minor (sneaker) males moved preferentially to ‘rich’ plots.

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    ‘Rich’ plots had more harems, but treatments did not differ in harem size.

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    Females in ‘poor’ plots laid their eggs in lower-quality oviposition sites.

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    Male and female behavioural plasticity influence the mating system organization.

The availability and spatial distribution of reproductive resources determine female distribution, thus affecting the organization of mating systems and the intensity of sexual selection. Females of the harvestman Serracutisoma proximum lay eggs on specific plant species, which are defended by males of the large morph (majors). After oviposition, females remain inside the major's territory, forming a harem, which may be invaded by males of the small morph (minors) to sneak copulations. We experimentally manipulated the availability of the plants used as oviposition sites, and investigated how it affected the mating system of S. proximum. Our results show that females and minors moved preferentially to plots with high plant availability. Plots with high plant availability had more harems, which were established on the preferred plants. In plots with low plant availability, many females laid eggs on plants where S. proximum clutches had never been observed previously, rather than choosing to be a part of a harem on a preferred plant. Harem invasions were accomplished by both minors and majors, and the frequency of harem invasions was not influenced by plant availability. Finally, male–male competition for harems and the potential for sexual selection were also not influenced by plant availability. Female plasticity in oviposition site use probably attenuates competition among majors, allowing males with poorly developed weaponry to establish a territory and achieve copulations. Minors apparently adjust their distribution in response to harem density, but the income of minors does not increase the frequency of harem invasions in plots with high plant availability. Plasticity in the major mating tactic probably accounts for the high frequency of harem invasions, regardless of plant availability. We argue that behavioural plasticity may thus profoundly affect our ability to make predictions about the effects of oviposition site limitation on mating systems and the intensity of sexual selection in species exhibiting resource defence polygyny.

Section snippets

Study Site

We conducted the study at Intervales State Park, an area of Atlantic Forest in the state of São Paulo, southeastern Brazil. The region has high precipitation (2000–3000 mm/year) and average annual temperature between 17 °C and 19 °C. The climate is subtropical, with a warm-wet season from October to March and a cold-dry season from April to September. We studied a population of S. proximum living on the vegetation flanking the stream that follows the Caçadinha Track (24°14′S, 48°04′W; Fig. 1a).

General Description of the Data

In the 2011–2012 breeding season, we marked a total of 139 females, 99 major males and 45 minor males in the study area. In the peak of this breeding season, between February and March 2012, we observed 33 harems with a total of 64 egg-guarding females. During this period, 70% of the clutches were laid in rich plots and 30% in poor plots. Eleven clutches were laid in buffer areas, all of them in rocks or plants with SPQ = 0. These clutches were not included in the analyses reported in the

Discussion

Here we experimentally manipulated the natural availability of the plants used by S. proximum females as oviposition sites, and investigated how it affected the mating system and the intensity of sexual selection in this harvestman over two consecutive breeding seasons. We found that females and minor males moved preferentially to plots with high host plant availability, while no directional movement pattern was detected for major males, which is partially consistent with prediction 1. We also

Acknowledgments

We are grateful to the staff of Intervales State Park for logistic support, to Pedro P. Bueno and Louise Alissa for helping in the fieldwork, to Sara Mortara for helping in the identification of some fern species, to Bruno A. Buzatto for helping in the analysis of male morph discrimination and for revising a previous version of the manuscript, to Ayana B. Martins for revising the methods section, and to two anonymous referees who made useful comments on the manuscript. The authors are supported

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