Mating Biology Research Articles

Genetics of Hybrid Incompatibility Between Lycopersicon esculentum and L. hirsutum

We examined the genetics of hybrid incompatibility between two closely related diploid hermaphroditic plant species. Using a set of near-isogenic lines (NILs) representing 85% of the genome of the wild species Lycopersicon hirsutum (Solanum habrochaites) in the genetic background of the cultivated tomato L. esculentum (S. lycopersicum), we found that hybrid pollen and seed infertility are each based on 5-11 QTL that individually reduce hybrid fitness by 36-90%. Seed infertility QTL act additively or recessively, consistent with findings in other systems where incompatibility loci have largely been recessive. Genetic lengths of introgressed chromosomal segments explain little of the variation for hybrid incompatibility among NILs, arguing against an infinitesimal model of hybrid incompatibility and reinforcing our inference of a limited number of discrete incompatibility factors between these species. In addition, male (pollen) and other (seed) incompatibility factors are roughly comparable in number. The latter two findings contrast strongly with data from Drosophila where hybrid incompatibility can be highly polygenic and complex, and male sterility evolves substantially faster than female sterility or hybrid inviability. The observed differences between Lycopersicon and Drosophila might be due to differences in sex determination system, reproductive and mating biology, and/or the prevalence of sexual interactions such as sexual selection.

Bumblebees as model organisms to study male sexual selection in social insects

Social-insect males are often regarded as being merely short-lived "flying sperm containers", which ignores their potential influence on females and paternity patterns as found in other animals. Consequently, social-insect males have received only marginal attention and sexual selection has almost never been studied in these species. Here I present a review of the mating biology of bumblebees (Bombus spp.), which are the best-studied social insects to date. I follow a male's pathway from his birth until he successfully contributes to the next generation, and show that males have evolved adaptations and behaviors to influence paternity patterns at various stages of their life, which are similar to those exhibited by males of non-social insects. By comparing the available bumblebee data with more sparse studies of male reproductive behavior in other social Hymenoptera, I argue that such male adaptations may indeed be widespread in social insects. I suggest that current paradigms on sexual selection should be challenged by using social insects as model systems, because they offer unique features, and a solid theoretical background in which clear predictions can be made and appropriate experimental tests of them can be designed.

The mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis

1. Quantitative aspects of the mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis, including duration and frequency of mating, duration of various phases of the oviducal cycle, egg production rate and adult longevity were studied under laboratory conditions. One set of copepods was fed the alga Chlamydomonas reinhardtii whose density was adjusted to 2 × 105 cells mL−1 (about 10 mg C L−1), another set was fed a mixed diet consisting of natural plankton (copepod nauplii, small rotifers and large algae) in the size range of 50–150 μm (dry mass approximately 90 mg L−1).2. The entire mating process, from the grasping of the female by the male’s right geniculate antennule to the separation of the pair, lasted about 2 min. Spermatophore placement started at about 30 s to 1 min after mating began and took approximately 1 min. Immediately after the spermatophore had been fixed in the female’s genital segment, the pair separated.3. The total oviducal cycle, including the gravid phase where the female carried ripe oocytes and the non‐gravid phase where the female did not carry ripe oocytes, lasted about 5–6 days. The non‐gravid phase was particularly long; it was longer than the gravid phase and constituted 62–72% of the total cycle.4. Mating and spermatophore placement usually occurred with gravid females although occasionally (in 30 of 200 observations) spermatophores were attached in the genital segment of non‐gravid females. Generally two to four, but up to seven, spermatophores were observed at a female’s genital segment at the same time.5. Clutch size, rate of egg production and adult longevity depended on food. When fed on C. reinhardtii, females carried 7–8 eggs clutch−1, produced a mean of 1.3 clutches and lived 14 days on average. When fed natural mixed food, females carried 10 eggs clutch−1, produced 5.6 clutches and lived 37 days on average.6. Removal of males after the first clutch resulted in no further egg production. Re‐mating is necessary in E. gracilis for continuous clutch production and the production of fertile eggs.7. Mating duration is comparatively short and the non‐gravid phase comparatively long in E. gracilis. This could be an adaption to the life in the pelagic zone of the lake, where fish predators are present. Fish select ovigerous females, pairs in copula and, probably, females with ripe oocytes which make them conspicuous. Thus, a short mating duration and a prolonged period without conspicuous oocytes, can be advantageous.

Mating in a communal bee, Andrena agilissima (Hymenoptera Andrenidae)

Males of the fossorial, communal bee Andrena agilissima (Scopoli 1770) typically search for mates at flowers from which females collect pollen (WESTRICH 1989). To investigate whether communal nesting also affords mating opportunities for adults freshly eclosed from brood cells, we collected and dissected females that were emerging for the first time in spring from their natal nests and examined the contents of their spermathecae. Circa 97% of females contained spermatozoa in their spermathecae, indicating a high frequency of preemergence intranidal mating. Bees also copulated above ground, both near nest entrances and at flowers. In the latter situation, pollen-collecting females were seen to copulate, suggesting that A. agilissima females mate repeatedly (polyandry) and are sexually receptive across adulthood. The schedules of emergence of males and females from natal nest entrances in spring overlapped to a large extent; the species was neither markedly protandrous nor protogynous on the island of Elba, Italy, in 1998. These emergence patterns are consistent with both pre-emergence intranidal mating and polyandry linked to female receptivity extended across adulthood. The sex ratio at emergence was female biased (numerical proportion of males, M/M + F = 0.38), consistent with the view that pre-emergence intranidal mating generates local mate competition amongst males, and that it is an important component of the mating biology of A. agilissima. The mating opportunities of sons within the nest may potentially provide a selective benefit to communal nesting by females.

Mating expenditures reduced via female sex pheromone modulation in the primitively eusocial halictine bee, Lasioglossum ( Evylaeus ) malachurum (Hymenoptera: Halictidae)

The present paper reports on behavioral ex- periments and gas chromatographic analysis of chemical communication in the mating biology of the primitively eusocial sweat bee Lasioglossum (Evylaeus) malachurum. In a dual-choice experiment, a female made odorless was significantly less attractive than an untreated one. At- traction in L. (Evylaeus) malachurum is therefore medi- ated by a female-produced sex pheromone. Further bioassays showed that unmated gynes are more attrac- tive to males than mated ones. Males are able to dif- ferentiate between the two groups of females as little as 3 h after mating. Biotests with different samples ob- tained from attractive gynes showed surface extracts to be most attractive. Behavioral tests with synthetic copies of the compounds identified as cuticular constituents of virgin gynes were highly attractive to males; the volatile bouquets consisting of n-alkanes, n-alkenes and iso- pentenyl esters of unsaturated fatty acids were the most attractive samples. Isopentenyl esters of unsaturated fatty acids were the key compounds in inducing male inspections as well as stimulating pounces and copula- tory attempts. Virgin and nesting gynes differed clearly in the relative and absolute amounts of the volatiles on the cuticle. The total amount of volatiles was signifi- cantly higher in virgin gynes and decreased in breeding queens. Hydrocarbons were the dominant group of

Differential dispersal and female‐biased sex allocation in a parasitic wasp

1. Differential dispersal of males and females from a population is predicted to result in biased sex‐allocation decisions, even in the absence of sibmating.2. Mated Bracon hebetor Say (Hymenoptera: Braconidae) females produce distinctly female‐biased sex ratios (≈ 30% male), yet sibmating is not a feature of the mating biology of this species. Therefore the dispersal behaviour of male and female B. hebetor from caged subpopulations was examined.3. A higher proportion of females than males dispersed from the caged subpopulations. Furthermore, females dispersed earlier than males. This suggests that the level of competition for mates experienced by males is higher than the level of competition for hosts experienced by sisters.4. Roughly half of the dispersing females left after they had mated. Females generally mate once in their lifetimes, suggesting that competition between brothers for mates may be high.

Patterns of pair formation and mating in an ectoparasitic caligid copepod Lepeophtheirus salmonis (Krøyer 1837): implications for its sensory and mating biology

Non–invasive observations of single cohort and manipulated populations of the sealouse on laboratory–maintained salmon established the sequence of reproductive events and mating. Protandry occurs with adult male emergence synchronized with pre–adult II female emergence, the stage at which most pair formation and pre–copular guarding takes place. Male competence for pair formation and mating was achieved within 24 h of the final moult and pairing occurred according to the preference hierarchy, virgin adult females greater than pre–adult II females much greater than pre–adult I females. This hierarchy broke down when the adult male to unmated female ratio increased rapidly. Males mated successfully not only with newly moulted adult females, but also with older virgin females in which enlargement of the genital complex and premature extrusion of egg strings had occurred. Multiple mating by adult males was demonstrated and may be widespread. Significant inter–host transfer was also demonstrated. Adult males were more mobile than adult females and showed significantly more inter–host transfer. Ablation of the distal tip of the antennules significantly reduced the success of host–finding, pair formation and males' mating.

A case of multiple mating in stingless bees (Meliponinae)

In several stingless bee species many males aggregate in the vicinity of a nest when a virgin queen is present in the colony and is preparing for the nuptial flight. We report such male assemblage for Tetragonisca angustula. The departure of a virgin queen from the colony and the subsequent mating could be video-recorded, because the queen and the males that had mounted her fell to the ground. Since at least two males had lost their genitalia, multiple mating seems to have occurred. This is in contrast with the prevailing view found in literature concerning the mating biology of stingless bees.

Behaviour of drones in Melipona (Apidae, Meliponinae)

The behaviour of drones of different species of Melipona was studied in Costa Rica and on Tobago. Drones of all species behaved very similarly. The intranidal behavioural analysis indicates that drones spent most time on standing, walking, stirring the antennae and self-grooming. The only "typical worker behaviour", occasionally performed by 16 to 18 days old drones of Melipona, was the participation in nectar dehydrating. The age-relatedness and location in the nest where a behaviour is performed is being discussed. Worker aggression against drones was observed only three times. The behaviour of drones when they leave the nest is described. Drones leave the nest mainly between 8 and 11 AM, at an average age of 18.6 days. It was observed that drones do not return after they have once left the hive. A description is given of a nest-associated drone aggregation of Melipona fasciata on a wall. Drones of this species stayed in the aggregation for an average of 7.6 days, spending most time on standing or flying in a "cloud" near the nest entrance. They spent about five hours daily on the average and may leave the aggregation temporary. Drones were able to live up to 74 days in a closed hive, the average being 45 days. Implications of drone behaviour for the mating biology of stingless bees are discussed.

Ontogeny of cephalic volatile patterns in queens and mating biology of the neotropical stingless bee, Scaptotrigona postica

Summary Chemical communication is an ancient yet still immensely important part of reproduction. Amongst all invertebrates, the most sophisticated “chemical languages” are used by social insects. Here the sex- and caste-specific pheromonal messages consist of multicomponent mixtures. In the neotropical stingless bee Scaptotrigona postica, an inhabitant of dense tropical rain forests, the cephalic volatiles of a queen transmit information on her reproductive status to males. A distinct ontogenetic pattern of the queen pheromone composition allows drones to discriminate receptive virgins which are then chased during the short nuptial flight through the forest understorey. By means of gas chromatographic/mass spectroscopic analyses, the numerous volatile compounds found in pentane extracts of individual bee heads could be identified. Qualitative as well as quantitative changes of these volatiles in the course of imaginal development could be determined, and bioassays with synthetic compounds were undertaken in order to decode the chemical signals used during the short encounter of a young queen and her mate.

Estimation of sperm numbers in insects by fluorometry

To facilitate the study of mating biology in the desert leaf-cutter antAcromyrmex versicolor, methods were developed that allowed storage and easy quantification of sperm samples collected from both male and female reproductive tracts. Sperm samples stored frozen were sonicated, stained with a fluorescent DNA stain, and the fluorescence emitted by the stained sperm heads was measured. The intensity of fluorescence was shown to be a linear function of the number of sperm in the sample as determined by counting.

Benthic Bees? Emergence Phenology of Calliopsis pugionis (Hymenoptera: Andrenidae) at a Seasonally Flooded Site

Ground-nesting Calliopsis pugionis Cockerell emerged from nests that had been underwater for at least 3 mo. There was a significant correlation of the duration of submergence and the date of emergence, perhaps because inundation lowered soil temperature or oxygen availability. This delayed emergence excluded many bees from a major source of their normal forage, which grew at higher elevations than the flooded site and, thus, had unchanged phenology. The percentage of males among emerging bees increased with time, which contrasts with the expected pattern based on the mating biology of this species. Excavations of nests suggest that the life cycle of this species is univoltine and strictly annual. These results are discussed in terms of the effect of environmental unpredictability on a species tracking evolutionary optima.

The evolution of conspicuous coloration in male three-spined sticklebacks: Contradictory results and conflicting studies

AbstractThe three-spined stickleback (Gasterosteus aculeatus L.) is perhaps one of the most studied species of fish with respect to its mating behavior and reproductive biology. This paper reviews several well-known experimental studies which have focused on the adaptive significance of the bright-red breeding coloration of male sticklebacks including the maintenance and loss of red coloration with respect to predation pressure, and the role of parasites in affecting coloration and mate choice. However, results from some recent studies tend to refute or draw into question these original results. The main reason for these conflicting and contradictory findings is not only because stickleback populations show a high degree of variability, as is often argued by stickleback biologists, but appears to be due to a lack of correspondence between laboratory and field work. It is proposed that factors affecting the mating and reproductive biology of three-spined sticklebacks in the wild may be much more complex th...

Alternative adaptations, sympatric speciation and the evolution of parasitic, inquiline ants

Inquiline ant species are workerless social parasites whose queens reproduce in colonies of other species alongside the host queens. Inquilines arise either when one non-parasitic species evolves into an inquiline parasite of another non-parasitic species (the interspecific hypothesis), or by the speciation of intraspecific inquilines from their host stock (the intraspecific hypothesis): it is unlikely that inquilines evolve from other forms of social parasite. This paper reviews the evidence for and against the inter-and intraspecific hypotheses. All inquilines are close phylogenetic relatives of their host species (loose ‘Emery's rule’), and some are their host's closest relative (strict ‘Emery's rule’). A problem for the interspecific hypothesis is how to explain the strict Emery's rule, because phylogenetic constraints on host choice are probably quite weak. By contrast, the intraspecific hypothesis has difficulty accounting for the parasites' sympatric reproductive isolation. Facultative polygyny, in which queens may found colonies alone or by adoption into an existing multi-queen colony, should promote the evolution of small intraspecific inquilines. This is because small colony-founding queens should preferentially seek adoption, which provides the opportunity to produce a sexual-only brood. We suggest that microgynes, i.e. miniature queens found in some polygynous ants, represent such parasites. We review the evidence that inquiline species have evolved intraspecifically from microgynes in Myrmica ants. The coexistence within a species of a monogynous (singly-queened) and a polygynous form is probably a phenomenon usually unconnected with inquiline evolution. The reproductive isolation of intraspecific inquilines plausibly arises from divergent breeding behaviour associated with the parasites' small size. Such divergence could involve either a temporal separation in mating episodes, with small parasites maturing early, or a spatial separation, with small males being sexually-selected to mate near the nest with small queens seeking adoption, instead of in mating aggregations. We conclude that inquiline species strictly following Emery's rule could have evolved by the intraspecific route. If so, such species provide evidence for West-Eberhard's “alternative adaptation” hypothesis that between-species diversity frequently stems from diversity within species. They also represent likely cases of sympatric speciation. We suggest work on the parasites' phytogeny, genetics, behaviour and mating biology to test these conclusions further.

HOST-PLANT-INDUCED ASSORTATIVE MATING IN ENCHENOPA TREEHOPPERS.

The hypothesis tested here is whether extrinsic host-plant-induced life-history timing and mating biology promote assortative mating along host-plant lines. In the arboreal, univoltine Enchenopa treehopper system, host plants mediate the timing and synchronization of egg hatch. The result is a uniform age structure with a restricted mating window during which females mate once. Enchenopa on host plants that differ in phenology have asynchronous life histories and mating windows, suggesting that temporal differences may promote assortative mating. To test this hypothesis, egg hatch of Enchenopa from the same host-plant species was manipulated to produce continuous adult age-classes. Under experimental conditions with no spatial barriers, mating occurred between individuals similar in age. The mechanism promoting this assortative mating is differential mortality in males and females, such that few males are still alive when females in successive age-classes mate. Such host-plant-induced assortative mating is viewed as an effective mechanism to protect the integrity of gene pools from migrants, permitting selection for host-plant-adapted genotypes and speciation.

The mating biology of a mass-swarming mayfly

The males of many species of mayflies form dense aggregations, or swarms, to which females come to mate, typically at specific landmarks. This mating system was investigated in Epeerus longimanus, a mayfly of the western United States that forms swarms that are quite large. Swarms were found to occur primarily in clearings along the study stream, and certain sections consistently supported large or small swarms. The number of males was correlated with clearing size; in addition, the numbers of males attracted to artificil markers (sheets of plastic in a nearby meadow) increased with marker size. Thus, display habitats appeared to be patchily distributed and to limit swarm size at least locally. Collections of emerging nymphs demonstrated no association with swarm locations. Since adult mayfiles do not feed, it is evident that swarm locations are not explainable as feeding or emergence sites, but they do correlate with landscape features. The number of observed matings per swarm event was generally 5–20% of the estimated peak male density, despite a sex ratio at emergence of 1·2 males: 1 female. Survivorship of caged males and recaptures of marked males both indicate the likelihood that males are sufficiently long-lived to joins swarms on successive evenings, which may account for the low frequency of matings. The role of mate location in the evolution of swarming behaviour is discussed.

The role of learning in the mating biology of a sweat bee Lasioglossum zephyrum (Hymenoptera: Halictidae)

Results from experiments on the role of learning in the mating biology of a sweat bee, Lasioglossum zephyrum (Hymenoptera: Halictidae), are described in this paper. Male learning of individual female odors is important in natural populations (Table 1), as has been shown in the laboratory. Four other hypotheses are unlikely to account for the observed behavior: (1) Female odors dissipate rapidly; (2) Males learn and then avoid the study area; (3) Males or females produce repellents which are effective against other males; or (4) males recognize their own odor on previously-contacted females, which they subsequently avoid. Regarding questions of “male preference” and “optimal outbreeding,” Tables 2 and 3 show there are no consistent preferences for more novel or less novel female odors.

Foraging, Grooming and Mate-seeking Behaviors of Macropis nuda (Hymenoptera, Melittidae) and Use of Lysimachia ciliata (Primulaceae) Oils in Larval Provisions and Cell Linings

The first demonstrated use of floral oils in nest cell linings and pollen provisions is reported here for the bee Macropis nuda (Melittidae). The floral oil chemistry is closely analogous to the cell-lining lipids secreted from the Dufour's glands of many other bee genera. Details of oil and pollen collection and transfer behaviors at Lysimachia ciliata are compared with those of other bee taxa. The simultaneous pollen and oil collection behaviors are reminiscent of Melitta buzz pollination (sensu Buchmann, 1978). Aspects of the mating biology, including hind leg posturing to advertise mating nonreceptivity, are also discussed.

Observations on Male Territories in a Carpenter Bee, Xylocopa (Neoxylocopa) hirsutissima Maidl (Hymenoptera, Anthophoridae)

AbstractObservations were made on territoriality of ♂♂ of the Brazilian carpenter bee Xylocopa hirsutissima. These territories are found on mountain tops where the ♂♂ hover from 4–6 p.m. in close vicinity of an optical beacon, being a protruding shrub or little tree. Territories are defended against other ♂♂Production of a pheromone by the mandibular glands is supposed. This territoriality as well as that of other species of the genus is considered to be an important aspect of the mating biology.

Further Observations On the Function of Male Territories in the Carpenter Bee Xylocopa (Neoxylocopa) Hirsutissima Maidl (Anthophoridae, Hymenoptera)

Territorial behaviour of male X. hirsutissima was studied. Depending on wind direction the male establishes a territory on or near the mountain top where he hovers behind or in a little shrub, protected from the wind and facing away from the shrub. With the aid of the legs, the mandibular gland secretion appears to be distributed over the ventral side of the abdomen. This secretion serves as a sex pheromone. Small insects approaching the male evoke pre-copulatory behaviour. Females fly upwind towards the male and appear to land on the shrub, immediately behind the males hovering place. Mating occurs or is initiated at this site. The mating biology of X. hirsutissima is compared with that of some other species within the genus and a basic similarity is noted.