Testing the role of same-sex sexual behaviour in the evolution of alternative male reproductive phenotypes

Abstract

Male same-sex sexual behaviour (SSB), where males court or attempt to mate with other males, is common among animal taxa. Recent studies have examined its fitness costs and benefits in attempts to understand its evolutionary maintenance, but the evolutionary consequences of SSB are less commonly considered. One potential impact of SSB might be to facilitate the evolution of traits associated with less sexually dimorphic males, such as alternative reproductive tactics, by diverting costly aggression from other males. To test this, we capitalised on the recent rapid spread of a silent male morph of field cricket, Teleogryllus oceanicus, which is unable to produce characteristic male acoustic signals, benefits from satellite mating behaviour, and exhibits feminised appearance and cuticular hydrocarbon profiles. We tested the prediction that interactions involving these non-signalling, less sexually dimorphic male morphs would show heightened rates of SSB, which could reduce the strength of male-male competition and permit greater access to females. We found no evidence that SSB was more common in trials involving silent males. Instead, SSB was predicted by courtship of females presented during a pre-trial treatment. Our results provide evidence supporting the view that SSB represents a spillover of sexually selected courtship behaviour in a non-adaptive context, but do not support a strong role for SSB in the evolution of less ornamented males in this system.

Can behaviour impede evolution? Persistence of singing effort after morphological song loss in crickets

“…In both Kauai and Oahu, flatwing segregates as a singlelocus X-linked trait [10,24]. Silent males are strongly disadvantaged in the context of sexual selection [26,27], but the phenotype nevertheless spread rapidly under selection from the fly. Flatwing males are capable of expressing the precise patterns of rhythmic forewing movement that produce song in normal-wing males [11].…”

The role of intrasexual competition on the evolution of male-male courtship display: a systematic review

“…However, only five of the experimental studies explicitly tested hypotheses for male-male courtship display. Four of the studies tested the intrasexual competition hypothesis ( Boutin et al, 2016 ; Lane et al, 2016 ; Kuriwada, 2017 ; Rayner & Bailey, 2019 ), and two found evidence to support it ( Lane et al, 2016 ; Kuriwada, 2017 ). Further, a single study tested another hypothesis but ended up suggesting competition ( Abbassi & Burley, 2012 ).…”

“…Different mechanisms of intrasexual competition were suggested in the experimental studies ( Table 2 ): male-male courtship display can be relevant for “resource defence” ( Elie, Mathevon & Vignal, 2011 ; Abbassi & Burley, 2012 ); it plays a role on “condition assessment” of the displayer or its opponents ( Abbassi & Burley, 2012 ); and males assess the displayer condition to modulate aggressiveness ( Lane et al, 2016 ; Kuriwada, 2017 ) by “diverting costly aggression” ( Rayner & Bailey, 2019 ), or to establish “dominance hierarchies” ( Oliveira & Almada, 1998 ; Ungerfeld, Ramos & Bielli, 2007 ; Wang et al, 2011 ; Ungerfeld et al, 2014 ); with dominant males performing more male-male courtship than subordinate ones ( Adachi & Soma, 2019 referring to Langmore & Bennett, 1999 ).…”

“…Concerning adaptive explanations, the intrasexual competition hypothesis was the most frequently suggested: we found 14 studies describing 20 species. However, only four studies formally tested this hypothesis ( Boutin et al, 2016 ; Lane et al, 2016 ; Kuriwada, 2017 ; Rayner & Bailey, 2019 ), from which only two found evidence to support it ( Lane et al, 2016 ; Kuriwada, 2017 ). Therefore, our first review highlights the need to empirically test the intrasexual competition hypothesis in more species with male-male courtship display.…”

Ancestral sex-role plasticity facilitates the evolution of same-sex sexual behavior

“…Such sexual mimicry might coevolve with SSB because SSB can also reduce aggressive interactions during competition (44,45; but see ref. 46). However, same-sex tandems in termites are not likely to be directly comparable to alternative mating strategies such as those based on deception, because heterosexual pairing is the highest fitness option for all termites and represents a cooperative relationship.…”