Combined cues of male competition influence spermatozoal investment in a moth

Abstract

1. Male animals usually raise their sperm allocation after detecting sperm competition risk. To date, only a few studies have investigated the cues used by males to sense

Pupal Cues Increase Sperm Production but Not Testis Size in an Insect

“…These findings indicate that juvenile male insects can predict future sperm competition risks from cues of conspecific immature stages and subsequently adjust their sperm production [17,19,[69][70][71]. In lepidopteran insects, adults [10] and pupae (current study) adjust production of both fertile eupyrene and infertile apyrene sperm, while larvae only fine-tune production of eupyrene sperm [19] in response to socio-sexual environments. Furthermore, larvae either increase [17,40] or reduce [19] testis size in response to larval cues but pupae (Figure 3) and adults do not change their testis size under different socio-sexual situations.…”

“…Evidence shows that most adult morphological traits are formed during the larval stage [42,43,47,48], allowing the larvae but not pupae and adults to adjust their testis size. Lepidopteran males produce most eupyrene sperm during the larval and pupal stages, most apyrene sperm during the pupal stage [53] and continue to produce both types of sperm during the adult stage [10]. Therefore, male larvae can donate varying portions of testis volumes to spermatogenesis and other functions [41], and trade off testis size and apyrene sperm production to increase eupyrene sperm production in response to increasing sperm competition risk [19].…”

“…Animals adjust their resource allocation strategies to maximize their reproductive fitness in response to socio-sexual environments [1][2][3]. For example, male animals may invest more in sperm after they detect the presence of rivals to gain an advantage in sperm competition [2,[4][5][6][7][8][9][10]. In insects, males fine-tune their sperm investment in response to sex specific cues experienced during the adult stage [10][11][12][13][14][15][16] or non-sex specific cues during the Insects 2021, 12, 679 2 of 9 larval stage [17][18][19][20][21].…”

“…For example, male animals may invest more in sperm after they detect the presence of rivals to gain an advantage in sperm competition [2,[4][5][6][7][8][9][10]. In insects, males fine-tune their sperm investment in response to sex specific cues experienced during the adult stage [10][11][12][13][14][15][16] or non-sex specific cues during the Insects 2021, 12, 679 2 of 9 larval stage [17][18][19][20][21]. Although insect pupae do not feed and crawl, they can communicate with each other using species-specific acoustic [22][23][24][25][26][27][28][29] or chemical cues [30][31][32][33][34].…”

“…The apyrene-to-eupyrene ratio remains consistent under food shortage during the larval stage [61] or environmental stress during the larval [62] and pupal stages [63]. However, E. kuehniella males increase the ratio after detecting rival cues during the adult stage [10] or reduce it following exposure to larval cues during the larval stage [19]. So far, it is still unclear whether the socio-sexual environment during the pupal stage affects the sperm production ratio.…”