Mating success and energetic condition effects driven by terminal investment in territorial males of a short‐lived invertebrate

Abstract

Summary1. The terminal investment hypothesis has two predictions: in the face of an infection (i) mature males will increase investment to traits that increase mating success, while such investments will occur to a less extent in young males; and (ii) physiological costs of resource reallocation will be more severe for infected mature males than for infected young males. 2. Although these predictions have been tested in long-lived vertebrates, prior studies have not examined actual resource allocation conflicts. Here, we have tested the above predictions and have investigated the energetic costs of increased mating by old males, using a short-lived invertebrate, the damselfly Hetaerina americana. Males of this species defend territories as the main way to obtain access to females. 3. Using groups of infected vs. noninfected males of two different ages, we found that compared to young infected males, mature infected males defended territories for longer, had higher mating success and directed agonistic behaviour to conspecific males more frequently. Despite similar immune responses by mature and young males, infected mature males ended up with less fat reserves compared to infected young males. This suggests that resource allocation conflicts are more severe for mature than for young males. 4. In general, these results suggest that the terminal investment hypothesis applies in males of short-lived invertebrates and that a cause of increased mating success for males of advanced ages is reduced energetic stores.

Female choice for sick males over healthy males: Consequences for offspring

“…Evidence for the terminal investment comes not only from other animals (e.g., Copeland & Fedorka, ; González‐Tokman, González‐Santoyo, & Córdoba‐Aguilar, ) but also our study species (Kivleniece et al, ; Krams et al, ). For example, experimentally infected male damselflies tend to defend their mating territories for longer compared to non‐infected males (González‐Tokman et al, ). Thus, infected males increased their chances to mate although they lived less than non‐infected males (González‐Tokman et al, ).…”

The effect of male-male competition and ornament size on mean and variance of courtship intensity towards heterospecific and conspecific females

“…However, when territorial males became non-territorial, their hybridization propensity did not decrease, but remained high. This could represent some terminal effect of compensating the low residual reproductive value of males who have lost their territory and are unlikely to regain it (Clutton-Brock 1984, Forsyth and Montgomerie 1987, Candolin 1999, Koskimaki et al 2004, González-Tokman et al 2013. The observed courtship patterns are not due to any intrinsic differences in reproductive activity between males following different tactics, since the conspecific courtship intensity was always high and similar between males.…”

Influence of mating and age on susceptibility of the beetle Anoplophora glabripennis to the fungal pathogen Metarhizium brunneum

“…We did not however find a cost of reproduction for Old females and we found that susceptibility to M. brunneum changes with age in unmated males. In other systems there is evidence that investments in immunity can change over the course of an invertebrate's lifespan (González-Tokman et al, 2013;Izhar and Ben-Ami, 2015). Maehara and Kanzaki (2014) also found that newly emerged adult Japanese pine sawyers (Monochamus alternatus) were more susceptible than 14 day-old beetles to the fungal pathogen Beauveria bassiana, although the authors did not test if this trend was the same for both male and female beetles.…”

“…Maehara and Kanzaki (2014) also found that newly emerged adult Japanese pine sawyers (Monochamus alternatus) were more susceptible than 14 day-old beetles to the fungal pathogen Beauveria bassiana, although the authors did not test if this trend was the same for both male and female beetles. Mature male damselflies (Hetaerina americana) maintained their reproductive efforts when a nylon thread was implanted while younger males decreased their reproductive efforts when encountering the same challenge; the thread had been inserted to challenge the immune system (González-Tokman et al, 2013).…”