Between fighting and tolerance: reproductive biology of wingless males in the ant Cardiocondyla venustula

Abstract

Male reproductive tactics vary widely across the species of the ant genus Cardiocondyla, from obligatory lethal combat among co-occurring males to complete mutual tolerance. The African species C. venustula Wheeler, 1908 has an intermediate phylogenetic position between taxa with fighting males and taxa with tolerant males and also shows an intermediate male behavior. Males from 2 native populations in South Africa and a population introduced to Puerto Rico attacked and killed freshly eclosing rivals but rarely engaged in deadly fights with adult competitors. Instead, several males per colony established small "territories" in their natal nests and defended them against other males. Males with a stable territory had more contact with female sexuals than nonterritorial males and more frequently engaged in mating attempts. In controlled choice experiments, female sexuals did not show any preference for particular males. We suggest that male territoriality in C. venustula is an adaptation to the seasonal production of large numbers of female sexuals by multiple mothers.

Population and colony structure of an ant with territorial males, Cardiocondyla venustula

“…Field studies gave conflicting results concerning queen number: while Wheeler [24] reported on regular singlequeening in an introduced population in Puerto Rico, our own observations revealed the regular presence of multiple queens per colony both in introduced and native populations [23,25]. The finding of dense populations of C. venustula near Pretoria and Bergville, South Africa, allowed us to conduct detailed analyses of the genetic structure of colonies and populations and how they are influenced by male territoriality and female dispersal on foot.…”

“…Winged queens have regularly been observed to disperse on foot, and some of them may enter and mate in alien nests, similar to what has been observed in Palearctic Cardiocondyla [30,44]. Wingless males of C. venustula may therefore not only compete for mating with their sisters [22,23] but also for mating with alien queens. The presence of multiple fertile queens in field and also lab colonies (unpublished data) suggests that C. venustula is facultatively polygynous, in contrast to the obligatorily monogynous Palearctic clade.…”

“…Thus, each female sexual was provided with simultaneous access to two males until it was mated. Mating events are inconspicuous and difficult to observe [23]. We therefore waited for several days until all queens had shed their wingswhich they usually do only after matingand then stored them in 100% before genotype analysis of stored sperm following Lenoir et al [30].…”

“…Behavioral studies revealed that males of C. venustula are always ergatoid and show an "intermediate" behavior between fatal fighting and complete tolerance: they defend small areas in the nest against nestmate males, engaging in regular, but typically non-lethal fighting with nestmate males [22,23]. Female sexuals (young, winged queens) were observed interacting with several males, but it remained unclear if they mated multiply.…”

Fighting and aggressive sound determines larger male to win male‐male competition in a bark beetle

“…Fighting is costly in terms of energy use, time, injury risk, increased risk of predation, and may even result in death (Kelly & Godin, 2001; Briffa & Elwood, 2004; Arnott & Elwood, 2009). Selection should favor accurate gathering of information to enable tactical decision‐making (Parker, 1974; Arnott & Elwood, 2008; Jacobs & Heinze, 2017). Some traits, including both static traits (such as body size) and dynamic traits (such as behavior) may function as an indicator of fighting ability, and honest signaling may reliably convey the condition or status of individuals (Hill, 1991; Eldred et al ., 2016; Yasuda & Koga, 2016; Alvarez et al ., 2017).…”