Audience effect is context dependent in Siamese fighting fish, Betta splendens

Investigations of communication networks in animals have focusedprimarily on determining whether animals extract informationfrom peripheral contests (eavesdropping) or respond to the presenceof bystanders (audience effect). The possibility that an animal'sresponse to being watched might be context dependent, however,has been explored in far less detail. This study investigatedthe influence of two contexts, exposure to audiences of differentsexes and presence or absence of a nest, on the aggressive behaviorof interacting male Siamese fighting fish, Betta splendens.Males interacted in the presence (male, female) or absence ofan audience in three different nest conditions (0, 1, or 2 nests).Audience sex and territorial status influenced aggressive behaviorin the interacting males, but a strong audience x nest interactionalso was uncovered. Males were more aggressive when neithermale had a nest and a male audience was present than when afemale or no audience was present. Males also were more aggressivewhen only one male had a nest and a male audience was presentthan when a female or no audience was present. When both maleshad nests and a male audience was present, however, males wereless aggressive than when only one male or neither male hada nest. In sum, aggressive behavior was influenced by the interactionbetween audience and nest; neither nest nor audience alone wassufficient to explain the results. Male Siamese fighting fishalter their behavior based on both external cues, the sex ofthe audience, and internal cues, reproductive state and resourcepossession. Our results emphasize the importance of consideringaspects of an animal's environment when examining audience effectsand communication networks in general.     

Putative chemical inhibition of development by conspecifics in mosquitofish, Gambusia affinis

The objective of this study was to test for a chemical influence of adult Gambusia affinis on the development and maturation of juveniles. Sixty juveniles (<1 day old) were reared (from a total of 157 trials) individually up to 115d in 3liter containers that circulated water bathing either (1) two adult males, (2) two adult females, (3) an adult male and an adult female, or (4) conspecific-free tank water. Randomly chosen juveniles were sampled over time, sacrificed, sectioned, and measurements were taken of standard length and gonadal parameters such as gonad size, number of spermatogenic cysts, or number of oocytes. Measurements were regressed as functions of time, and analyzed for significant differences by ANCOVA. A total of 32 males and 28 females were examined. Males showed no significant differences in any of the parameters, but females showed reduced growth rate and smaller ovary size when reared in water bathing two adult females. Mortality rate in these young fish was high, but Chi-square analysis showed that mortality rate was significantly higher when they were raised in water bathing at least one adult female. Females are known to influence female development in other vertebrates; our findings suggest this may also be true for a fish, and that the interaction may be through chemical communication.     

Court Like You Mean It: Male Siamese Fighting Fish are Less Attentive to Courting Males that Have Been Exposed to an Estrogen Mimic

Endocrine disrupting chemicals (EDCs) are ubiquitous in aquatic ecosystems where they have adverse effects on exposed organisms. In addition to causing physiological changes, EDCs often target fitness‐related behaviors such as locomotion and courtship. Ethinylestradiol (EE2) is an estrogen mimic that has been found to reduce courtship and aggression in males. However, the consequences of these reductions are not always explicitly addressed. One way in which EE2 may lead to decreased fitness occurs when males respond differently to exposed vs. unexposed conspecifics. To examine this, video playback was used to determine whether male Siamese fighting fish, Betta splendens, respond differently to exposed and unexposed males. Males were presented with four different combinations of videos of males played simultaneously: exposed swimming and unexposed swimming, exposed courting and unexposed courting, unexposed courting and unexposed courting, and exposed courting and exposed courting. Males directed more behaviors to the unexposed than the exposed courting male when presented simultaneously, likely because these unexposed males were perceived as a greater threat to mating success. Additionally, males spent more time tracking and gill flaring, two behaviors that are indicative of fight intent, when presented with two courting unexposed males. This combination could be considered the most threatening because there are two rival vigorously courting males present. These results suggest that EE2 exposure could result in exposed males receiving decreased attention from other males. However, since EE2 exposure also decreases competitive and courtship abilities, this would be far outweighed by the costs.     

Genetic architecture of sensory exploitation: QTL mapping of female and male receiver traits in an acoustic moth

The evolution of extravagant sexual traits by sensory exploitation occurs if males incidentally evolve features that stimulate females owing to a pre‐existing environmental response that arose in the context of natural selection. The sensory exploitation process is thus expected to leave a specific genetic imprint, a pleiotropic control of the original environmental response and the novel sexual response in females. However, females may be subsequently selected to improve their discrimination of environmental and sexual stimuli. Accordingly, responses may have diverged and the original genetic architecture may have been modified. These possibilities may be considered by studying the genetic architecture of responses to male signals and to the environmental stimuli that were purportedly ‘exploited’ by those signals. However, no previous study has addressed the genetic control of sensory exploitation. We investigated this question in an acoustic pyralid moth, Achroia grisella, in which a male ultrasonic song attracts females and perception of ultrasound likely arose in the context of detecting predatory bats. We examined the genetic architecture of female response to bat echolocation signals and to male song via a cartographic study of quantitative trait loci (QTL) influencing these receiver traits. We found several QTL for both traits, but none of them were colocalized on the same chromosomes. These results indicate that – to the extent to which male A. grisella song originated by the process of sensory exploitation – some modification of the female responses occurred since the origin of the male signal.     

Trees to treehoppers: genetic variation in host plants contributes to variation in the mating signals of a plant‐feeding insect

Community genetics research has demonstrated ‘bottom‐up’ effects of genetic variation within a plant species in shaping the larger community with which it interacts, such as compositions of arthropod faunas. We demonstrate that such cross‐trophic interactions also influence sexually selected traits. We used a member of the Enchenopa binotata species complex of treehoppers (Hemiptera: Membracidae) to ask whether male mating signals are influenced by host plant genetic variation. We reared a random sample of the treehoppers on potted replicates of a sample of host plant clone lines. We found that treehopper male signals varied according to the clone line on which they developed, showing that genetic variation in host plants affects male treehoppers' behavioural phenotypes. This is the first demonstration of cross‐trophic indirect genetic effects on a sexually selected trait. We discuss how such effects may play an important role in the maintenance of variation and within‐population phenotypic differentiation, thereby promoting evolutionary divergence.