Cuticular profiles and mating preference in a slave-making ant

The remarkable ability of slave-making ants to integrate chemically in the colonies of their host species makes them useful model systems for investigating the role of cuticular hydrocarbons in chemical recognition. The purpose of our study was to examine the influence of the rearing host species on the cuticular hydrocarbon profile and on the mating behaviour of sexuals of the slave-making ant Chalepoxenus muellerianus. Sexuals from a population parasitizing exclusively the host species Temnothorax unifasciatus were reared in the laboratory either with their natural host or another potential host species, Temnothorax recedens. C. muellerianus males reared with T. unifasciatus investigated and mounted female sexuals reared with the same host significantly more often than female sexuals reared with T. recedens. Similarly, C. muellerianus males reared with T. unifasciatus discriminated against female sexuals from natural T. recedens colonies. Males experimentally or naturally reared with T. recedens did not clearly discriminate between female sexuals reared by the two host species and only rarely engaged in mating attempts with either type of female sexuals. Chemical analyses showed that host species affect the chemical profile of C. muellerianus sexuals and vice versa. Our findings indicate that cuticular hydrocarbons might be important in the mating success of this ant species. Received 21 June 2006; revised 20 February 2007; accepted 1 March 2007.     

Mating biology and population structure of the ant, <Emphasis Type="Italic">Leptothorax gredleri</Emphasis>

Summary Female sexuals of the ant Leptothorax gredleri attract males by sexual calling. In an experimental set-up allowing for competition among males, both female and male sexuals copulated with up to four partners, with the median being one mate in both sexes. Neither male nor female sexuals invariably mated with the first partner they encountered, but we could not find any morphological difference between sexuals that succeeded in mating multiply and those that copulated only once. Males did not aggressively compete for access to the female sexuals. According to microsatellite genotyping, workers produced by multiply mated queens were all offspring of a single father, i.e. queens appear to use sperm from a single mate to fertilize their eggs. Population genetic studies revealed a strong population subdivision, suggesting that both male and female sexuals mate in the vicinity of their maternal nests and that gene flow is strongly restricted even between forest patches isolated only by a few meters of grassland.     

THE EVOLUTION OF ALTERNATIVE REPRODUCTIVE TACTICS IN MALE CARDIOCONDYLA ANTS

Alternative reproductive tactics are often associated with discontinuous variation in morphology but may evolve independent from each other. Based on life‐history data and a phylogeny we examine how male morphology and reproductive behavior are linked in the evolution of the ant genus Cardiocondyla. Wingless Cardiocondyla males engage in lethal fighting for access to female sexuals, whereas winged males disperse and mate away from the nest. This basic pattern shows considerable variation across species. A phylogeny based on ～3 kbp sequence data shows that male diphenism and lethal fighting are ancestral traits tightly linked in evolution. Winged males were lost convergently in several species groups, apparently in response to the low probability of encountering female sexuals in nests without a resident fighter male. An early dichotomy separates two clades with alternative male morphologies and fighting behavior, but phenotype and fighting strategy are not correlated with the presence of winged males.     

Production of winged and wingless males in the ant, <Emphasis Type="Italic">Cardiocondyla minutior</Emphasis>

Summary Wingless (ergatoid) males of the tramp ant Cardiocondyla minutior attack and kill their young ergatoid rivals and thus attempt to monopolize mating with female sexuals reared in the colony. Because of the different strength of local mate competition in colonies with one or several reproductive queens, we expected the production of new ergatoid males to vary with queen number. Sex ratios were mostly female-biased, but in contrast to the sympatric species C. obscurior (Cremer and Heinze, 2002) neither the percentage of ergatoid males nor of female sexuals among the first 20 sexuals produced varied considerably with queen number. As in C. obscurior, experimental colony fragmentation led to the production of winged males, whereas in unfragmented control colonies only ergatoid males eclosed.Received 3 December 2003; revised 20 February 2004; accepted 23 February 2004.     

The cost of males in Daphnia pulex

Sex is paradoxical, because asexuals should replace their sexual ancestors by avoiding the demographic cost of producing males (hereafter referred to as the cost‐of‐males). Despite the large body of theoretical and empirical work dealing with the paradox of sex, the cost‐of‐males assumption has been rarely tested. In the present study, we tested the cost‐of‐males assumption in the cladoceran Daphnia pulex. Populations of this species consist of both cyclically parthenogenetic (i.e. sexuals) and obligately parthenogenetic (i.e. asexuals) lineages. In addition, some of the asexual lineages produce only female offspring, whereas others produce functional males, which can mate with sexual females. We compared the reproductive investment of sexuals, male‐producing asexuals, and non‐male‐producing asexuals when raised separately under various environmental conditions. We also determined the outcome of competition between pair‐wise combinations of these reproductive modes. The cost of males was evident when sexual and asexual females were raised separately: sexuals produced fewer female offspring. However, there was no cost of males when reproductive modes were raised in pairs, as sexuals won the competition with asexuals. Our results directly relate to the field conditions experienced by D. pulex. Sexuals might suffer the cost of males at the beginning of the season, when resource competition is low; but when conditions deteriorate as the population approaches carrying capacity, sexuals seem to be better competitors in spite of male production.     

Species-Specificity of Chemical Signals: Silk Source Affects Discrimination in a Wolf Spider (Araneae: Lycosidae)

Female spiders deposit chemical cues that elicit male courtship behavior with silk. These cues are often assumed to be species-specific although male spiders may court in response to chemical cues of closely-related species. We used behavioral assays to test the extent of species discrimination of female chemical cues by male Schizocosa ocreata, a wolf spider (Lycosidae). Discrimination, expressed as relative courtship intensity of males, varied significantly with phylogenetic distance. Males did not discriminate between female cues of conspecifics and a sibling species, S. rovneri. Courtship response was intermediate for another species within the ocreata clade and not different from control for spiders outside the clade. These findings support the sibling species status of S. ocreata and S. rovneri, and also suggest the composition of female chemical signals is conserved across closely related wolf spider species.     

Growth and survivorship as proximate causes of sexual size dimorphism in peninsula dragon lizards Ctenophorus fionni

Males and females differ in body size in many animals, but the direction and extent of this sexual size dimorphism (SSD) varies widely. Males are larger than females in most lizards of the iguanian clade, which includes dragon lizards (Agamidae). I tested whether the male larger pattern of SSD in the peninsula dragon lizard, Ctenophorus fionni, is a result of sexual selection for large male size or relatively higher mortality among females. Data on growth and survivorship were collected from wild lizards during 1991–1994. The likelihood of differential predation between males and females was assessed by exposing pairs of male and female lizards to a predator in captivity, and by comparing the frequency of tail damage in wild‐caught males and females. Male and female C. fionni grew at the same rate, but males grew for longer than females and reached a larger asymptotic size (87 mm vs. 78 mm). Large males were under‐represented in the population because they suffered higher mortality than females. Predation may account for some of this male‐biased mortality. The male‐biased SSD in C. fionni resulted from differences in growth pattern between the sexes. The male‐biased SSD was not the result of proximate factors reducing female body size. Indeed SSD in this species remained male‐biased despite high mortality among large males. SSD in C. fionni is consistent with the ultimate explanation of sexual selection for large body size in males.     

Alternative mating tactics of the gobiid fish <Emphasis Type="Italic">Bathygobius</Emphasis><Emphasis Type="Italic">fuscus</Emphasis>

The reproductive ecology of the gobiid fish Bathygobius fuscus was studied at Nobeoka, Miyazaki, Japan. Males of this species maintain small rock holes as a nest and females spawn an egg mass on the wall of the nest. The males employed two forms of mating tactic: nest holding and sneaking. A nest holder stayed in the nest and waited for a female to visit, whereas a sneaker intruded into a nest while a pair was engaged in reproduction. Males larger than 55 mm standard length were always nest holders; those of smaller size employed both tactics. As the larger males excluded the smaller males, the latter did not occupy a nest hole. With a decrease in the number of larger males, smaller males changed their mating tactic from sneaking to nest holding. The results suggest that male Bathygobius fuscus adopt a conditional strategy whereby they change their tactic depending on their social status. Electronic Publication     

The influence of hybridization on colony structure in the ant species Temnothorax nylanderi and T. crassispinus

The parapatric sibling ant species Temnothorax nylanderi and T. crassispinus hybridize in the contact zone in the Franconian Jura, Southern Germany. Aim of our study was to investigate the impact of hybridization on colony composition and fitness. We classified colonies as either ‘pure’ or containing hybrids by determining their allozyme pattern at GPI, an enzyme that is fixed for different alleles in the two parental species, and quantified their reproductive output. Most colonies with hybrid workers had a T. crassispinus queen. Colonies with heterozygous, hybrid workers produced more young workers than colonies of the parental species but similar numbers of male and female sexuals. Female sexuals from colonies with heterozygous workers had a significantly lower weight than female sexuals from pure colonies. Only a single reproductive queen was found to be heterozygous, suggesting reduced fitness of hybrid queens. As in the parental species, hybrid colonies appear to be frequently taken over by alien queens, which obscures the genetic colony structure. Received 6 April 2006; revised 10 June 2006; accepted 15 June 2006.     

Chemically-mediated pre-mating behavior in two tetranychid species

We used bioassays to evaluate the arrestment response of male twospotted spider mite, Tetranychus urticae Koch, and Banks grass mite, Oligonychus pratensis (Banks) to whole-body extract from conspecific quiescent deutonymphs. We examined the effect of previous behavior on mite response to extract from female quiescent deutonymphs. We also examined male arrestment and guarding behavior in response to 2 extract concentrations and to extract from male quiescent deutonymphs. Male T. urticae and O. pratensis exhibited similar changes in their behavior in response to the different extracts with which we presented them. Males that were guarding quiescent deutonymphs immediately prior to testing spent more time in an untreated 3.5-mm-diameter circle than did males that were previously engaged in other behaviors. However, when nonguarding males were presented with extract of conspecific female quiescent deutonymphs they remained in the stimulus circle as long as guarding males did in an untreated circle. Arrestment duration of nonguarding males increased at 2 higher extract concentrations. The arrestment response was not exclusive to extracts from female quiescent deutonymphs; nonguarding male mites were also arrested by extracts from male quiescent deutonymphs, although for a shorter time. Duration of arrestment was related roughly to size differences between male and female quiescent deutonymphs. Furthermore, males did not show an exclusive preference for guarding conspecific male or female quiescent deutonymphs. It seems unlikely that the arrestant is a specific sex pheromone. Rather, male mites probably use the arrestant as a necessary cue to focus their attention on an individual that may be a suitable mate. Other tactile, visual, and chemical stimuli may then help males to decide whether to remain and assume mate guarding behaviors.     

Sexual selection versus alternative causes of sexual dimorphism in teiid lizards

Summary The presence and extent of sexual dimorphisms in body form (size and shape) of adult macroteiid lizards were investigated. Males were significantly larger than females in the temperate species, Cnemidophorus tigris, and in the tropical species, Ameiva ameiva and C. ocellifer. Young adult C. tigris males grew faster than young adult females within and between reproductive seasons. Adult males of all species had larger heads than adult females of the same body size; this difference increased with body size. Moreover, male C. tigris were heavier than females of the same snout-vent length. The causes and consequences of the sexual dimorphisms were also examined. The possible causes of body size are especially numerous, and distinguishing the relative influences of the various causal selection factors on body size is problematical. Nevertheless, observational field data were used to tentatively conclude that intrasexual selection was the cause of larger body size of C. tigris males relative to females because (1) larger males won in male aggressive interactions, (2) the winning males gained access to more females by repelling competitors and by female acceptance, (3) larger males consequently had higher reproductive success, and (4) other hypothetical causes of larger male size were unsupported.     

Mate Choice by Both Sexes Maintains Reproductive Isolation in a Species Flock of Pupfish (Cyprinodon spp) in the Bahamas

Female and male mate choices can reinforce reproductive isolation after sympatric speciation. Using a binary choice design, we examine the importance of visual cues in female mate choice in all three sympatric species of pupfish on San Salvador Island. We also examine the importance of olfactory cues in female choice of the hard‐shelled invertebrate specialist (Cyprinodon brontotheroides). We examine male mate choice in two of the three species, the scale eater (C. desquamator) and the detritivore (C. variegatus). Females of all three species use visual cues and prefer conspecific males. C. brontotheroides females do not use olfactory cues to discriminate between conspecific and heterospecific males. Males of C. desquamator and C. variegatus also preferentially court conspecific females. Thus, mutual mate choice, where both females and males exhibit mate choice, acts as a strong behavioral pre‐mating isolation mechanism in these sympatrically speciated pupfish.     

A novel sexual pattern in serranid fishes: simultaneous hermaphrodites and secondary males in Serranus fasciatus

Synopsis Gulf of California populations of Serranus fasciatus are composed of functional simultaneous hermaphrodites and males. This is the first serranid known to have this sexual pattern which is functionally intermediate between the typical serranid patterns of simultaneous and protogynous hermaphroditism. Males of S. fasciatus are derived from hermaphrodites by resorption of ovarian tissue and proliferation of the extant testicular band. Distinct sexual roles are evident in spawning events. Hermaphrodites gain female function by pair spawning with males (124 and 125 observed spawns) and rarely with other hermaphrodites (1 of 125). Hermaphrodites gain male function by sneak spawning (9 of 125) and rarely by pair spawning with other hermaphrodites. Males exclusively pair spawned with hermaphrodites. Despite its unusual sexual pattern, S. fasciatus appears allied with other Serranus species based on similarities in gonad morphology.     

The Resource-Based Mating System of the Mediterranean Pollen Wasp Ceramius fonscolombei Latreille 1810 (Hymenoptera, Vespidae, Masarinae)

Males of C. fonscolombei patrol and perch at water collection sites or at plants of Reseda, both of which are important resources for female brood care. The mating system can be classified as resource defense polygyny modified by the existence of alternative male mating tactics. Occupying temporary territories at watercollection sites constitutes the primary tactic which is more profitable for larger males. The secondary tactic of patrolling at flowers provides a nonaggressive alternative through which smaller males gain at least some mating success. Males at water collection sites occupy considerably smaller ranges but spend a higher proportion of time patrolling than males at flowers. They frequently grapple with other males, an activity that is absent at flowers. Males at water collection sites copulate about 2.5 times more frequently than males at flowers. The copulation frequency of the males at water collection sites is positively correlated with their body size, while copulation frequency is negatively correlated with body size at flowers. Males patrolling at water collection sites and males patrolling at flowers do not differ in body size, indicating that the decision between alternative mating tactics is not made relative to body size but is influenced by other factors.     

Species recognition by male swordtails via chemical cues

Species recognition can often play a key role in female matingpreferences. Far less is known about conspecific mate recognitionfrom the male perspective. In many closely related taxa, femalesexhibit few obvious visual differences and males might haveto attend to chemical cues in mate recognition, a possibilitythat has rarely been explored in vertebrates. Here, we examinemale species recognition via odor cues in the swordtail fish,Xiphophorus birchmanni. In dichotomous choice experiments wefirst tested whether males respond to female odor cues. We foundthat males were attracted to conspecific female odor and thoseof a related allopatric congener, Xiphophorus malinche, overa water control. Males did not, however, respond to the femaleodor of the more distantly related sympatric platyfish, Xiphophorusvariatus. We then gave male X. birchmanni the choice betweenconspecific and heterospecific female stimuli. Males, in thisscenario, significantly preferred the conspecific odor whenthe alternative was platyfish. However, when offered odor cuesof X. malinche, male X. birchmanni actually preferred the heterospecificfemale cue. The complex array of preferences reported here,previously documented only in females, underscores the needto consider the behavior of both sexes in dictating actual matingoutcomes.     

Do social environments affect the use of exaggerated traits in the dobsonfly Corydalus bidenticulatus?

Male–male competition is strongly affected by female presence. In insects with primitive features such as megalopterans, however, it is not known how aggressiveness is expressed in the context of female presence. Here we examined the effect of social environments on the use of secondary sexual traits in the sexual behavior of the Mexican dobsonfly Corydalus bidenticulatus (Megaloptera: Corydalidae). Males of this species have exaggerated traits such as disproportionally elongated mandibles with no dentition, which is a secondary sexual trait used in competition over female access as well as males of other Corydalus species. We investigated how male–male interactions are carried out, and the scaling relationships of sexual and non‐sexual traits. Our results show that males of C. bidenticulatus are not indiscriminately aggressive. The decision whether to fight or not is affected by their social environments: males are aggressive against other males only when the presence of a female is detected. Results also suggest that mandibles and antennae are sexually dimorphic, being exaggerated and showing positive allometry only in males. In contrast, male genitalia, a sex‐specific trait, show negative allometry.     

Different positions of males approaching towards females and male choices between webs with and without stabilimentum in a sexually cannibalistic orb‐web spider,Argiope bruennichi

Males of the orb‐weaving spider species Argiope bruennichi (Araneidae) are frequently victims of sexual cannibalism. Therefore, a male spider approaching a female should have strategies to avoid being killed before copulation. Our present field study detected six types of A. bruennichi male positions vis‐à‐vis the female web. In 78% of situations (39/50), only one male attached to a female. Two males attached to the same female in 11 cases. We observed no cases of three or more males on the same female web. We most commonly observed the situation of a male staying in its own web and connecting to a female's web with its silk thread (46% of cases). Of the female webs chosen by males, 68% were decorated with both an upper and lower portion of stabilimentum – a conspicuous white silk structure that reflects much more ultraviolet light than other spider silks in the web. Only 14% (7/50) of the selected webs lacked stabilimentum. Therefore, we conducted an experiment to investigate the males' choice between females' webs with and without stabilimentum. Of the 24 males used in the experiment, 10 chose webs with stabilimentum. This result did not show a strong preference of the male for stabilimentum between equally sized webs, and thus did not support an earlier suggestion that stabilimentum in A. bruennichi might function to guide males to females for mating.     

Ultrasound hearing and male–male communication in Australian katydids (Tettigoniidae: Zaprochilinae) with sexually dimorphic ears

The genus Kawanaphila (Tettigoniidae: Zaprochilinae) is unusual among the Tettigoniidae in the possession of sexually dimorphic auditory organs. We examined the auditory system and acoustic behaviour of two previously unstudied species in this genus to test whether reduced hearing in males is consistently associated with reduced male–male competition. Kawanaphila yarraga (Rentz, 1993) and K. mirla (Rentz, 1993) are both sexually dimorphic with respect to their auditory system, but to different degrees. Males of both species produce songs consisting of trains of brief (< 1 ms) pure-tone sound pulses at ultrasonic frequencies (K. yarraga, 40 kHz;K. mirla, 70 kHz). In both species, female hearing is more sensitive than that of males by 10 dB. In addition, male K. mirla are most sensitive at lower frequencies than females. Male and female K. yarraga differed only in sensitivity, not in tuning. The two species also differ in their degree of sexual dimorphism in auditory anatomy. Kawanaphila mirla males lack some auditory specializations of the prothoracic tracheal system, which are present in the normal tettigoniid condition in females. In K. yarraga males these structures are present, but reduced in size relative to females. The acoustic behaviour of males of the two species is consistent with this pattern of relative auditory sensitivity. Males of both species interact acoustically by altering the timing of their sound output to synchronize with neighbouring males. However, K. mirla males only interact in this way over very short distances (< 5 m), whereas K. yarraga males interact with neighbours up to at least 10 m distant. These results indicate that, although males of the two species differ in hearing sensitivity, the nature of their responses to conspecific calls are similar to one another and to those of other acoustic insects. This suggests that acoustically mediated male–male competition may be maintained even while selection favours a reduction in male auditory sensitivity.     

Variance in male reproductive success and sexual size dimorphism in pinnipeds: testing an assumption of sexual selection theory

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