Iporangaia – Body condition affecting mating success and parenting behavior

Description

Other

Funding provided by: Fundação de Amparo à Pesquisa do Estado de São Paulo
Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100001807
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Methods

General description of the experiments

We performed two experiments in which we manipulated the body condition of both non-parental and parental I. pustulosa males, subsequently recording their mating success and number of acquired eggs under natural field conditions. Upon collecting males from the field, we transported them to the laboratory, where they were individually marked with enamel ink. This procedure does not appear to influence the behavior of the individuals (e.g., Requena et al. 2009, 2012; Requena & Machado 2015). Given that harvestmen have very low basal metabolism (Santos 2007), their body condition declines slowly under resting conditions. To accelerate this process, we experimentally forced all males to decline their body condition through a series of physical exercises (i.e., forced walking) in the laboratory. Only after the forced exercise, when we were able to decline the body condition of all males, we assigned them to one of two experimental groups: (a) 'good condition' group, in which males received water and food ad libitum, and (b) 'poor condition' group, in which males received water ad libitum but no food. We allowed males of the 'good condition' group to feed for one day, sufficient to induce significant food intake and, consequently, a marked increase in body condition (Fig. S1 in Supplementary Material). The criteria used to assign males to each of the two experimental groups are presented in Table S1 and Figs. S2-S4.

After the manipulation of body condition, we returned each male to the exact location of capture within our transects. During subsequent visits to the field, a team of four researchers actively surveyed the transects for three consecutive days. They searched for marked males during the afternoon (between 14:00 h and 18:00 h) and the night (between 20:00 h and 00:00 h). During each inspection visit, we recorded whether the recaptured males were successful or unsuccessful in acquiring eggs. To ensure that males were not tending to any clutches, upon encountering a marked male, we carefully searched the vegetation within a 2-meter radius around him. Given that males significantly reduce their movement while caring for eggs (Requena et al. 2012), this searching procedure allowed us to confirm whether a male was unsuccessful in acquiring eggs. For successful individuals, we took photographs of their broods to quantify the number of eggs acquired during the sampling interval, which spanned from one inspection visit to the next.