Resource availability as a proxy for terminal investment in a beetle

Abstract

Terminal investment hypothesis is a longstanding theoretical idea that organisms should increase their reproductive effort as their prospects for survival and reproduction decline. However, numerous attempts to test the terminal investment in reproduction have yielded contradictory results. This study reports an experimental confirmation of the terminal investment hypothesis. It was predicted that immune-challenged yellow mealworm beetles (Tenebrio molitor) are more likely to follow terminal investment strategy when their food resources are limited. Our results suggest the key role of food resources while making decisions to follow a terminal investment strategy. We found that male individuals invested in their sexual attractiveness at the expense of immune response and survival when food was not available. In contrast, the beetles did not decrease their lifespan and did not invest in the attractiveness of their sex odours under conditions of food ad libitum. Our results show the importance of food availability and quality in understanding the evolution of reproductive strategies.

A dark cuticle allows higher investment in immunity, longevity and fecundity in a beetle upon a simulated parasite attack

“…Although cuticular darkening and encapsulation response may compete for the same limiting resources necessary for melanin synthesis, such as tyrosine, we did not find any costs associated with immune response, fecundity and longevity in females with black elytra. The availability of food is an important predictor of survival and reproductive strategies in T. molitor (Krams et al 2015). However, the access to tyrosine, a food-derived melanin precursor, was likely the same for dark and pale females in this study.…”

“…Males of many species tend to increase the number of copulations (Bateman 1948), and in case of terminal investment in reproduction male individuals may increase their sexual attractiveness at the expense of their longevity (Krams et al 2014b(Krams et al , 2015. In females, fitness is often positively linked to lifespan (Trivers 1972), while longevity largely depends on investment into immune function (Lin et al 1998;Krams et al 2014a).…”

“…Several studies on invertebrates have recently demonstrated the role of ecological conditions on trade-offs between immune function and fecundity (Zerofsky et al 2005), availability of food (Moret and Schmid-Hempel 2000;Krams et al 2014aKrams et al , 2015, especially nitrogen-rich proteins, lifespan (Ye et al 2009;Krams et al 2013b) and larval competitive ability (Kraaijeveld and Godfray 1997). Selection for increased cuticular melanization in mealworm beetles Tenebrio molitor resulted in an increase in immune response (Armitage and Siva-Jothy 2005).…”

Costs and benefits of vertical and horizontal transmission of Dengue virus

“…This could be due to the fact that infected daughters were exposed to infection during their entire lifetime, whereas infected mothers were exposed to infection only as adults. According to the hypothesis of terminal investment, organisms give priority to reproduction if they perceive that their survival is at risk (Krams et al, 2011(Krams et al, , 2015, and, possibly, infected daughters prioritized reproduction at the expense of survival. It is also likely that the effect observed in the daughters reflected a prior investment in them by their mothers, as it is known that the investment in a certain behavior or physiological response is not limited within generations but the cost could be paid across generations (Clutton-Brock, 1984).…”

The population determines whether and how life-history traits vary between reproductive events in an insect with maternal care

“…For instance, low food intake has been shown to inhibit the expression of terminal investment by females of the Alpine chamois Rupicapra rupicapra (Mason et al 2011), whereas food restriction and pathogen presence favoured its expression in males of the yellow mealworm beetle Tenebrio molitor (Krams et al 2015) and of the blue-footed booby Sula nebouxii (Velando et al 2006), respectively. Although environmental constraints often vary between populations, the occurrence of population-specific differences in the life-history traits expressed by individuals from early and late cohorts remains surprisingly poorly studied (see Mason et al 2011;Javoiš 2013;Vincze et al 2013).…”