Mate recognition in Acanthagrion truncatum (Odonata: Coenagrionidae)

Sexual and species recognition, along with sexual color dimorphism, play an important role in the reproduction of many animal species. In this article, it was investigated if males of the dimorphic Neotropical damselfly Acanthagrion truncatum are able to recognize mates and differentiate them between co-specific males and hetero-specific females of sympatric species. The results showed misguided mating attempts from males towards other males and Homeoura chelifera females. They also seem able to recognize A. lancea and Telebasis carmesina females as hetero-specifics. This study support the hypothesis that malemale interactions are misdirected sexual behavior and that sympatric morphologically similarspecies may represent visual interference for mate searching males.


Introduction
Sexual color dimorphism (SCD) is common among animals, resulted from male-male and malefemale interactions to signal the individual sexual identity (ANDERSSON, 1994).Such dimorphism is considered to be influenced by means of sexual selection and male-male competition (DARWIN, 1871;ANDERSSON, 1994), resulting in a crucial part of animal reproduction: mate recognition.
Coenagrionidae damselflies often exhibit SCD, usually with bright colored males and cryptic females (CORBET, 1999).Most of them are not territorial, with a few exceptions (e.g.GUILLERMO-FERREIRA; DEL-CLARO 2012) and do not present courtship behavior.Male-male interactions are considered to be a mate recognition mistake, because males interact with other males as if they were females in an attempt to mate with them.The presence of sympatric coenagrionids may also result in intense interference visual signals that may pose another problem for mate-searching males (MILLER;FINCKE, 1999).Thus, in this paper, it was investigated if males of the coenagrionid Acanthagrion truncatum Selys, 1876 are able to discriminate between co-specific males and females and hetero-specific females.

Study species
Acanthagrion is a neotropical genus, widespread in Brazil, where 22 of the 41 described species can be found.They are common in still waters and ponds, perching on aquatic vegetation.Acanthagrion truncatum males present blue-black body coloration, while females are yellowish-green-black.see below) were tethered to a line and presented to seven individual A. truncatum males at the pond, they were allowed to 'fly' in front of the males and perch.This method is widely used with Odonata (FINCKE, 1994;MILLER;FINCKE, 1999;GUILLERMO-FERREIRA;BISPO, 2012).The male response was recorded according to three categories: (1) approach; (2) hover; and (3) grab tandem -1 ; assuming that, these categories show a progressive scale of more intense sexual response.Males that did not respond (N = 31, 22% of tested males) were excluded from the analysis.The following co-specific males and females, and sympatric Coenagrionidae hetero-specific females were presented: Acanthagrion lancea Selys, 1876, Homeoura chelifera Selys, 1876 and Telebasis carmesina Calvert, 1909.Data were analyzed with Chi-square tests with Yates correction using the program Statistica 9 ® (STATSOFT, 2009).

Discussion
The field data showed that A. truncatum males are able to recognize the females of the congeneric A. lancea and the ones of T. carmesina as being different from their mates.However, A. truncatum males confounded H. chelifera females as being co-specific.The females of the latter species are blue and probably resemble A. truncatum males, which are also blue.Miller and Fincke (2004) indicated that heterospecific females may often be effective signal distracters for males, generating costs in sterile interactions.Additionally, these authors show how recognition among sympatric species may be under the influence of factors such as time of the day and the color morphism of each species.Hence, the results presented here may indicate that the level of heterospecificity in interactions and the level of distraction imposed by sympatric species depend on the color of their females, rather than their phylogenetic proximity.
The results also showed that males might have difficulties in distinguishing between co-specific males and females, behaving similarly in response to both.Gorb (1998) found that Coenagrion puella Linnaeus, 1758 males can distinguish males from females visually by morphological structures and coloration pattern.However, other studies have shown the difficulties males have to identify females.When searching for mates, males may take other males for females and try to mate with them (STOKS; DE BRUYN, 1998; VAN GOSSUM et al., 2005).The results presented here support the theory that male-male interactions in coenagrionids are misdirected mating attempts.
Several studies have shown possible causes and explanations for the failure in mate recognition in Coenagrionidae.Johnson (1964), for example, stated that male-male interactions in coenagrionids are a type of basal territorialism in odonates.However, this is very unlikely since most coenagrionids are non territorial and not site attached (CORBET, 1999).Miller and Fincke (1999), on the other hand, proposed the 'learned mate recognition' theory, which suggests that males must have a number of successful interactions with receptive co-specific females to learn how to recognize mates.Sexual recognition failure also occurs in other Odonata (e.g.Calopterygidae, KUITUNEN et al. 2012;Libellulidae, CORBET, 1999;BICK;BICK 1981;SCHULTZ;SWITZER, 2001;Aeshnidae, HACET, 2010).Recently, evidences have suggested that learned mate recognition can be a common system in this group (KUITUNEN et al. 2012), playing an important role in premating reproductive isolation.

Conclusion
In conclusion, we suggest that hetero-specific and male-male interactions in A. truncatum are driven by recognition failure during male mate recognition learning process.

Table 1 .
Acanthagrion truncatum male (N =109) responses (approach, hover and grab) to individuals presented to them (cospecific male and female, and hetero-specific females)