The Large Seed Size of Domesticated Lima Beans Mitigates Intraspecific Competition among Seed Beetle Larvae

Abstract

The domestication of beans has selected for larger seeds in cultivated plants compared to their wild relatives. This has not only resulted in an enhanced resource for humans, but also for the insects that feed on these seeds. Seed beetles that attack wild and cultivated seeds often lay several eggs on a single seed. We hypothesized that the larger seed size of domesticated beans will mitigate the competition among the larvae that hatch from these eggs, with important implications for their growth and survival. To test this we examined how seed size of wild and cultivated Phaseolus lunatus (lima bean) affect the performance of the Mexican bean weevil Zabrotes subfasciatus, an important pest of beans in Mexico. A negative correlation was found between the initial number of eggs on a seed and the weight of female beetles that emerged, but only for the much smaller wild seeds. Similarly, beetle survival was found to be negatively correlated with competition intensity only on wild seeds. Our results imply that by selecting for larger seeds, domestication of P. lunatus has reduced the intensity of intraspecific larval competition of Z. subfasciatus.

Host density and parasitoid presence interact and shape the outcome of a tritrophic interaction on seeds of wild lima bean

“…The reason for this is often related to the amount of resource available in larger seeds and the consequences on adult body size and ultimately their fitness 27 . Seed beetles lay several eggs on the same seed, which means that larval competition can be very intense and, as can be expected, is more significant in small seeds 25,26 .…”

“…Physical and chemical characteristics of the host seed are known to greatly affect beetle performance and behavior 21–24 . For example, numerous studies show that when faced with a choice, seed beetles prefer to oviposit on larger than smaller seeds 25,26 . The reason for this is often related to the amount of resource available in larger seeds and the consequences on adult body size and ultimately their fitness 27 .…”

“…For example, Campan and Benrey 35 found that the performance of the parasitoid Stenocorse bruchivora was better when it parasitized larger beetle larvae in cultivated seeds of Phaseolus vulgaris compared to smaller larvae in wild seeds. It is likely that the intraspecific competition among seed beetle larvae is relaxed in these larger cultivated seeds resulting in larger beetles 26 . The interactive effects of host density leading to intraspecific competition and the action of parasitoids have mainly been studied for their effect on host immune responses against endoparasitoids of caterpillars 37–39 .…”

Parasitoids of leaf herbivores enhance plant fitness and do not alter caterpillar‐induced resistance against seed beetles

“…Plant traits can affect seed beetle performance and evolution (Abdala‐Roberts & Mooney, ; Campan & Benrey, ; Cuny, Shlichta, & Benrey, ; Kergoat, Delobel, Fédière, Rü, & Silvain, ; Toju & Sota, ). More recently, studies showed how plant traits altered by interactions with leaf herbivores can subsequently affect the interactions with insects that attack flowers and seeds (Hernández‐Cumplido et al, ; McArt et al, ).…”

The interaction effect between intraspecific competition and seed quality on the life‐history traits of the seed‐feeding beetle Acanthoscelides macrophthalmus

“…On the other hand, smaller seeds should limit larval development, affecting adult body sizes, for example, suggesting that phenotypic changes in buchines may occur due to the variation in seed size. In fact, some studies have shown that seed size is an important source of phenotypic variation in seed beetles (Toquenaga & Fuji, ; Takakura, ; Amarillo‐Suárez & Fox, ; Cuny et al, ). In addition, the evolution of body size in bruchines can be mediated by the type of competition (scramble or contest) that takes place inside the seeds, which is directly related to the size of the seeds of the host plants (Messina & Karren, ).…”