DOI: 10.5061/dryad.hmgqnk9j6
title: Effects of biases in adult sex ratio and male body condition on the alternative reproductive tactics of a gift-giving spider

description: 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.
description: 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.
description: 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.