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Effects of biases in adult sex ratio and male body condition on the alternative reproductive tactics of a gift-giving spider

Citation

Tuni, Cristina et al. (2021), Effects of biases in adult sex ratio and male body condition on the alternative reproductive tactics of a gift-giving spider, Dryad, Dataset, https://doi.org/10.5061/dryad.hmgqnk9j6

Abstract

This dataset contains raw data from the manuscript entitled "Adult sex ratio and male body condition affect alternative reproductive tactics in a spider", from Daniel Heimerl, Pavla Dudová, Karoline Wacker, Elisa Schenkel, Garance Despréaux, Cristina Tuni, accepted for publication in the journal Behavioral Ecology

The study investigates how biases in adult sex ratios can affect mating tactics in a spider. Sex ratio variation can alter the intensity of sexual selection by enhancing competition for mates. Under intense competition males increase their investment in behaviors to outcompete rivals (e.g., fighting). Yet, given that in male-biased environments mating opportunities are rare males may alternatively reduce costly courtship and/or adopt alternative reproductive tactics (ARTs). Males of the spider Pisaura mirabilis adopt different mating tactics, offering females genuine nuptial gifts (prey), nutritionally worthless gifts (prey leftovers) or no gifts.

To test whether behavioral shifts between gift tactics are triggered by changes in the competitive environment, we established replicate spider populations under natural conditions (field enclosures) at varying adult sex ratios (male-biased, female-biased and equal) and sampled gift tactics (no gift, genuine and worthless gifts) repeatedly over time. We additionally explored how male individual traits, such as body size and condition, affect the expression of ARTs.

In male-biased populations males produced more gifts but of low quality, suggesting competition to trigger increased mating effort to ensure mate acquisition and fertilizations, but through a worthless gift tactic. Production of gifts and of genuine gifts was favored by high body condition, pointing to energetic limitations as being central for male reproductive capacity. We hence highlight two co-existing mechanisms at play to explain ARTs in this system, the competitive social environment where expression of gift tactics is based on optimal-decision making to overcome competition, and a conditional strategy linked to the individual’s energetic state.

Methods

We established replicate spider populations inside enclosures housed on the Ludwig Maximilians University's Biocenter. While keeping densities constant we established three adult sex ratios (male-biased, female-biased, equal sex ratio). We inspected each enclosure at regular intervals over the course of the breeding season, and scored occurrence and quality of male nuptial gifts. This was done, by scoring whether individually marked males were carrying a silk wrapped prey and by collecting animals to measure gift weight as an indication of quality, and male body mass to estimate male condition.

Data was processed by generalized linear mixed effects models (GLMM) using R.

Usage Notes

The readme file contains an explanation for each of the variables in the dataset, including measurement units. Information on how the measurements were taken can be found in the associated manuscript referenced above.