Interspecific Copulation Research Articles

Avian hybridization, mixed pairing and female choice

A review of behavioural studies of hybridization and mixed pairing in birds led to the following conclusions. (1) Hybridization is more common where one of two hybridizing species is rare. (2) There is no tendency in mixed pairs or in interspecific copulations for females to belong to a rarer species than males, as would be predicted by theory based on female choice. (3) There is no evidence that females prefer males of a larger species when hybridizing, in sympatric or in parapatric species. I propose three hypotheses to account for these findings. (1) Scarcity of conspecifics facilitates hybridization in general, no matter which sex is the rare one. (2) Mistakes in mate recognition cause hybridization, especially when females choose wrongly. (3) Supernormal stimuli may sometimes cause hybridization. It is not possible to judge which of these hypotheses is the best supported, and hybridization is likely to have multiple causes.

Frequency of interspecific matings and of hybrid offspring in sympatric populations of Viviparus ater andV. contectus (Mollusca: Prosobranchia)

In species pairs able to produce fertile hybrids, the amount of introgression can be limited by the frequency of interspecific copulations. We investigated the frequency of interspecific copulations between Viviparus ater and V. contectus and the proportion of hybrid offspring of V. ater females in natural populations in northern Italy. Although there was significant assortative mating, the frequency of interspecific copulations was substantial. At sites where V. contectus was rare, 5.9% of all matings, and up to 73% of matings in which V. contectus was involved, were interspecific. At sites where both species were abundant 14.8% of all matings were interspecific. Male–male matings occurred in approximately 3% of copulations. In 1993, 12 out of 325 V. ater females collected from 10 sympatric populations and held in isolation for two to five months gave birth to 25 hybrid offspring, out of a total of 2548 offspring produced by all females. The proportion of hybrid offspring (ranging from 0 to 2.3% depending on the site) was positively related to the proportion of V. contectus in the population. Since interspecific copulations are frequent and hybrid offspring are produced in nature, we conclude that assortative mating is not an effective isolating mechanism between V. ater and V. contectus.

Frequency of interspecific matings and of hybrid offspring in sympatric populations of Viviparus ater and V. contectus (Mollusca: Prosobranchia)

In species pairs able to produce fertile hybrids, the amount of introgression can be limited by the frequency of interspecific copulations. We investigated the frequency of interspecific copulations between Kviparus ater and V. contectus and the proportion of hybrid offspring of V. ater females in natural populations in northern Italy. Although there was significant assortative mating, the frequency of interspecific copulations was substantial. At sites where V. contectus was rare, 5.9% of all matings, and up to 73% of matings in which V. contectus was involved, were interspecific. At sites where both species were abundant 14.8% of all matings were interspecific. Male-male matings occurred in approximately 3% of copulations. In 1993, 12 out of 325 V. ater females collected from 10 sympatric populations and held in isolation for two to five months gave birth to 25 hybrid offspring, out of a total of 2548 offspring produced by all females. The proportion of hybrid offspring (ranging from 0 to 2.3% depending on the site) was positively related to the proportion of V. contectus in the population. Since interspecific copulations are frequent and hybrid offspring are produced in nature, we conclude that assortative mating is not an effective isolating mechanism between V. ater and V. contectus.

Interspecific Mating of Introduced, Sterile Bactrocera dorsalis with Wild B. carambolae (Diptera: Tephritidae) in Suriname: a Potential Case for Cross-Species Sterile Insect Technique

Copulation with sperm transfer was observed between the oriental fruit fly, Bactrocera dorsalis (Hendel), and the carambola fruit fly, B. carambolae (Drew & Hancock), in outdoor field cages in Suriname. Sterilized oriental fruit flies from Hawaii were shipped to Suriname for testing against wild carambola fruit flies to investigate whether the oriental fruit fly could be used in a potential sterile insect program against the carambola fruit fly. Of 217 total observed copulations on 5 test dates, 17 (7.8%) were interspecific, and 10 (4.6%) were of the crucial type, sterile oriental fruit fly ♂ × wild carambola fruit fly ♀. Interspecific copulations tended to be of short duration, especially when the male was an oriental fruit fly (i.e., average time in copula was 148.0 min for carambola fruit fly ♂ × oriental fruit fly ♀, whereas only 4.67 min for oriental fruit fly ♂ × carambola fruit fly ♀ at a 5:1 oriental fruit fly:carambola fruit fly ratio). Homogamic (like with like) pairings tended to be longer, especially for carambola fruit fly, with average times in copula of 115.7 and 481.4 min for oriental fruit fly ♂ × oriental fruit fly ♀ and carambola fruit fly ♂ × carambola fruit fly ♀, respectively. With both sexes present, oriental fruit flies began mating earlier in the evening (≈2,500-lux), whereas carambola fruit flies started mating at ≈300 lux. With only sterile male oriental fruit flies released, the proportion of interspecific pairs (oriental fruit fly ♂ × carambola fruit fly ♀) rose to return ⅓ of the total, at a sterile ♂: wild ♂ ratio of 5:1. This was 3-fold higher than for the release of bisexual oriental fruit fly. An index of mating isolation, relative isolation index, was high (>100, where random mating = 1) because of high assortative mating in the case of bisexual oriental fruit fly. Approximately 70% of carambola fruit fly females that copulated with carambola fruit fly males had sperm in their spermathecae. By comparison, 0% (0/6 flies) were mated in the case of carambola fruit fly ♀ mated to oriental fruit fly ♂ when both oriental fruit fly sexes were present, whereas 50% (2/4 flies) were mated when males-only oriental fruit fly were released.

Hybridization and speciation in the carabid beetles of the subgenusOhomopterus(Coleoptera, Carabidae, genusCarabus)

AbstractNatural hybridization among wingless carabid beetles of the subgenusOhomopterus(Carabidae, genusCarabus)is reviewed, and its significance in the evolution of this subgenus discussed. Natural hybridization occurs between parapatric species of similar size. Two case studies of natural hybridization suggest that natural hybridization could have affected the evolution of this subgenus in different ways. When there is a large difference in genital morphology between hybridizing species, interspecific copulation often results in genital injuries that causes mortality of copulating individuals, and hence reduces the fitness of hybridizing individuals greatly. In such a case, hybridization may be effective in maintaining the parapatric distribution of the two species, and in the long term, may promote reinforcement selection for traits which are effective in prezygotic reproductive isolation. When the morphological difference in genitalia is not so large as to cause genital injury, a hybrid population may be established at the intermediate zone between two parental species, provided that the immigration rates of the two species into the intermediate zone are small. Thus, natural hybridization may have contributed to both divergence and reticulate evolution in this subgenus.

GENITAL LOCK-AND-KEY AS A SELECTIVE AGENT AGAINST HYBRIDIZATION.

We demonstrate experimentally that differences in genital characters impose a direct cost of interspecific copulation on two closely related carabid species, Carabus (Ohomopterus) maiyasanus and C. (O.) iwawakianus, that share a narrow hybrid zone. Males of both species attempted copulation indiscriminately between conspecific and heterospecific females. Females experiencing heterospecific mating often suffered mortality due to rupture of their vaginal membranes. Those without fatal injury laid eggs which developed into F1 adults, but the fertilization rate was much lower than for intraspecific pairs. Males of C. maiyasanus, but not C. iwawakianus, often had broken genital parts (copulatory pieces) following interspecific copulations, which may prevent normal copulation in subsequent matings. Because of female mortality and low fertilization rate, the estimated fitness cost of interspecific mating was very large in terms of the reduction in the number of offspring (hatching larvae) for both sexes and both species. Thus, genital lock-and-key appears to exert significant selection against hybridization in the hybrid zone of these carabid beetles.

Heterospecific inter-pulse intervals of courtship song elicit female rejection in Drosophila biauraria

The present study investigated the significance of song in sexual isolation in Drosophila biauraria. Interspecific copulation was not observed with a heterospecific D. triauraria male that had intact wings, although it was often observed when the male's wings were removed, indicating that heterospecific courtship song elicits female rejection, and prevents copulation. Artificially synthesized songs were played to a female with a wingless, antennaless male. The conspecific inter-pulse interval of artificial song increased mating frequency, whereas the heterospecific, longer or shorter, inter-pulse interval significantly decreased the frequency. The mating frequency with random noise and silence showed intermediate values. Female rejection behaviour was greater with heterospecific than with conspecific inter-pulse intervals of artificial song; with random song and silence female responses were intermediate. This indicates that the inter-pulse interval is used as a species discriminator in D. biauraria females. It is suggested that the female's ability to discriminate inter-pulse intervals and her responses, rejection and acceptance, have evolved under the influence of reinforcement, reproductive character displacement, or both, which triggered sexual selection.

Intra- and interspecific copulations in the two congeneric green stink bugs,Nezara antennata andN. viridula (Heteroptera, Pentatomidae), with reference to postcopulatory changes in the spermatheca

Intra- and interspecific copulations betweenNezara antennata andN. viridula were investigated, with reference to postcopulatory changes in the spermatheca. The duration of copulation was significantly shorter in the case ofN. viridula males andN. antennata females than it was in the other 3 combinations. Both sperm and pulpy substance were transferred into the spermatheca during the intraspecific copulation of each species. No sperm was found in the spermatheca after interspecific copulation. However, the pulpy substance was found in the dilated portion of spermathecal ducts of someN. viridula females copulated with anN. antennata male, whereas no such substance was found in the case of theN. antennata females copulated with anN. viridula male. Most of the pulpy substance appeared to have been absorbed from the spermatheca within a 5-day period after the copulation. This absorption was observed for theN. viridula females copulated with anN. antennata male, as well as for the females of each of the species copulated with a conspecific male. It was suggested that this pulpy substance was a male-derived nutrient.

The Stereotyped Behavior of Sexual Cannibalism in Latrodectus-Hasselti Thorell (Araneae, Theridiidae), the Australian Redback Spider

This paper presents the first account of stereotyped behaviour in the practice of sexual cannibalism in any species. Cannibalism is achieved by female Latrodectus hasselti spiders, primarily because the copulatory orientation of the male in this species is unique and does not conform to the orthodox posture of males of other Latrodectus species. In this case, after penetration of the epigynum with one palpal embolus, the male turns a somersault through 180-degrees so that his abdomen comes to rest against the female's mouthparts, whereupon she begins to devour him. The cannibalistic process is slow and the male often succeeds in a second intromission with the other palp. The somersault is highly stereo-typed and predictable; it was observed in all 56 intromissions in the present study. The nuptial death risk to the male during copulation if both palps are employed is 0.66. However, even if he escapes copulatory demise he will die from his injuries within two days. Male Latrodectus hasselti can be mated with female L. katipo, an allopatric species native to New Zealand. Somersaulting by the male L. hasselti also occurs in this inter-specific copulation but the female L. katipo makes no attempt to devour him. It is concluded that male somersaults and female cannibalistic behaviour in L. hasselti are genetically programmed events.

Analyse expérimentale de l'isolement reproductif entre deux espèces jumelles et sympatriques d'araignées : le Lycosa thorelli (Keyserling) et le Lycosa carbonelli Costa et Capocasale

Four experimental groups were used: (A) males Lycosa thorelli × female L. thorelli; (B) male Lycosa carbonelli × female L. carbonelli; (C) Male L. thorelli × female L. carbonelli; (D) male L. carbonelli × female L. thorelli. Males were placed in a field with conspecific sexual pheromone and confronted to anesthetized virgin females. Male L. thorelli showed a greater tenacity than male L. carbonelli in the maintenance of the copulatory position. The typical copulation pattern (intraspecific groups) became atypical in interspecific groups. Only one typical interspecific copulation was observed in group C. Male L. carbonelli showed a good specific discrimination when mounting the female, while male L. thorelli showed a low discrimination level. The maintenance of the copulatory position could be determined by a modal number of ejaculations in the case of male L. carbonelli and by a modal duration in the case of male L. thorelli. Atypical copulations might indicate a mechanical incompatibility between the genitalia of the two species. Typical copulations produced offspring, indicating the absence of postcopulatory isolation mechanisms.

Introgressive hybridization in Heteroptera: the example of Limnoporus Stål (Gerridae) species in western Canada

Populations of the pondskaters, Limnoporous dissortis and Limnoporous notabilis, hybridize extensively in the Cordilleran region of western Canada. In laboratory crosses using L. dissortis from central Alberta and L. notabilis from southwestern British Columbia, most eggs are fertilized and begin development, but only ca. 50% of the eggs hatch and nearly all F1 hybrid adults are males. F1 hybrid males are fertile in backcrosses to females of both species, although egg hatch is reduced and mainly male progeny result from crosses to females of the paternal species. These species both have an XO sex chromosome system, and the foregoing results suggest that either products of genes on X chromosomes of the two species are incompatible or that they are incompatible with heterospecific cytoplasmic elements. Males of L. dissortis are more successful at interspecific copulations than are those of L. notabilis, perhaps because they more frequently adopt aggressive mating behaviour that circumvents premating barriers. Although gene pools of these two species are partially isolated by both pre- and post-mating barriers, there has been large-scale exchange of genes at autosomal loci, and significant introgression occurs over a large geographic area. Introgression is asymmetric, with genes of L. dissortis tending to flow disproportionately into L. notabilis populations, reflecting differences between the species in mating behaviour and dispersal tendencies. Because these two species are not closest relatives, I conclude that reticulations can be important considerations in the evolution of semiaquatic bugs. A literature survey shows that interspecific hybridization occurs in a number of heteropteran families, although partial barriers to gene flow are common.

Terminal steps in pheromone biosynthesis byHeliothis virescens andH. zea

In vivo application to the sex pheromone gland ofHeliothis Virescens andH. Zea of large quantities of alcohols normally present in small amounts resulted in the preferential conversion of the alcohols to the corresponding pheromonal aldehydes. Amounts of the minor component aldehydes were increased up to 15-fold by selectively applying large quantities of the alcohol precursors. Using this technique, we have inducedH. virescens to convert "bombykol," the sex pheromone of the silkworm, to the corresponding aldehyde, "bombykal," and have induced femaleH. zea to produce the same sex pheromone components used byH. virescens by applying tetradecanol and (Z)-9-tetradecenol to the surface of the gland. Further, treatedH. zea females were attractive toH. virescens males and caused males to attempt interspecific copulation repeatedly. We have also found that the enyzme involved in this conversion is dependent on the presence of molecular oxygen, indicating that a nonspecific alcohol oxidase is responsible for the terminal biosynthetic step in pheromone production by bothH. virescens andH. zea.

Laboratory Induced Hybridization of Two Crayfish Species, Orconectes Rusticus and O. Propinquus

ABSTRACT Laboratory induced interspecific copulations between the crayfish Orconectes rusticus and O. propinquus resulted in fewer broods and fewer Stage III juveniles per brood than did intraspecific copulations. Naturally occurring interspecific copulations should therefore affect the reproductive success of both species where they coexist, and may have contributed to the recent range expansion of O. rusticus.

Mating Behavior of the Oriental Fruit Fly, Dacus dorsalis HENDEL (Diptera : Tephritidae)

Mating behavior of the oriental fruit fly, Dacus dorsalis HENDEL, was studied under laboratory conditions. The precopulation period was quite variable and 29 days were needed for 50% accumulated mating. Ovaries developed with time, and mated females consisted of those with ovaries in an advanced stage of development. Courtship behavior and general pattern of the daily activity rhythm of the oriental fruit fly proved very similar to those of the melon fly, described in earlier studies. Interspecific copulation between two species was not observed.

Interspecific copulation in and co-occurrence of similar-sized freshwater centropagid copepods

Laboratory experiments were performed in which males of a given centropagid calanoid copepod species were placed with females of another species. Five interspecific pairings were tested, and in four of these, males attempted copulation or copulated with the partner of a different species. Metasome lengths of copepods in all populations used for experiments were determined: males attempted copulation with females whose average length was 0.88-1.09 times the normal size of the female for that species. These results imply that co-occurrence of similar-sized calanoids may be rare because of mating behaviour, temporal or spatial differences in mating, rather than because of competition for resources. A survey of reported co-occurrences of centropagid copepods in the genera Boeckella and Calamoecia found in Australia supports this contention.

Definition and revision of the Enoplognatha ovata (Clerck) group (Araneae: Theridiidae)

AbstractThe monophyletic Enoplognatha ovata group is defined on the basis of the following synapomorphic characters: subapical first metatarsal trichobothrium, sclerotized and modified apex of the conductor in the male palpal bulbus, and strongly developed copulatory pockets in the female vulva. In the group the male conductor and the female epigynal openings together with the copulatory pockets form a coadapted functional unit which might prevent interspecific copulation. The hitherto known range of the group covers the western Palaearctic and, apparently through recent introduction by man, the eastern and western Nearctic. Three species are included: E. ovata (Clerck) (Palaearctic, Nearctic), E. latimana n. sp. (southern Middle Europe, Nearctic) and E. penelope n. sp. (Mediterranean). The characteristics of the species are described and discussed both at the individual and population levels.

An Analysis of Copulatory Behaviour of Microtus Agrestis and M. Arvalis in Relation To Reproductive Isolation

AbstractA quantitative description of the copulatory behaviour of two species of closely related voles (M. agrestis and M. arvalis) is presented. Special attention is paid to the separate contributions of males and females to the time course of events in order to make predictions about the problems which would arise in interspecific copulation attempts. The species were similar with regard to mounting latency, number of ejaculations and durations of pauses between mounting series after ejaculation. Durations of mounting series were shorter in M. agrestis than in M. arvalis. The duration of a series is determined by the number and length of intermount intervals (IMIs) and nonejaculatory mounts and duration of the ejaculatory mount. The number of mounts was greatest and their duration was shortest in M. arvalis, leading to equal total mounting time in the two species. IMIs were longest in M. arvalis and, because the number was also greatest in M. arvalis, the total IMI time per series was longest in M. arvalis. Consequently, the mounting series was longest in M. arvalis. Durations of mounts were exponentially distributed; therefore, the tendency of males and females to terminate mounts could be estimated as constants. In both species, females showed a much higher tendency to terminate mounts than did males. In M. arvalis, both males and females showed higher termination tendencies than in M. agrestis. Males of the two species did not differ in their tendencies to terminate IMIs. Females of M. arvalis, however, aggressively resisted mounting more often than did M. agrestis females, leading to relatively long IMIs in M. arvalis. M. agrestis males often ejaculated during a single mount; M. arvalis males did so after at least five mounts. In accord with this species difference, it could be shown that mount terminations (or the experiences connected with them) negatively influenced the excitation state of M. agrestis males; i.e., the number of mounts prior to an ejaculation was greater (and the total mounting time was longer), the shorter the time the mounts lasted (i.e., the higher the females termination tendency was). In M. arvalis the number of mounts was smaller, the shorter the mounts lasted. In this species, high termination tendencies of the female correlated with much resistance to mounting (long IMIs). The combination of short mounts with long IMIs seems to have a positive influence upon the males. Thus, M. agrestis females delay ejaculation by a high termination tendency of mounts, whereas M. arvalis females seem to accelerate ejaculation by similar actions. Males and females appear to be very well adapted to each other: the M. agrestis female is relatively tolerant and the male ejaculates sooner, the more tolerant she is; the M. arvalis female is rejective and the male ejaculates sooner the more rejective she is, at least within the limits of rejectivity of the observed females. Females differ such that rejectivity in M. agrestis equals tolerance in M. arvalis, so that interspecific copulations are not likely to be successful. It is hypothesized that the rejectivity in M. arvalis fits in with the gregarious way of life of this species. For the female may select the fittest males and/or rejectivity by the female and the positive effect of it upon the male may serve as an incest preventing mechanism.

Reproductive Isolation and the Potential for Character Displacement in the Damselflies, Calopteryx Maculata and C. Aequabilis (Odonata: Calopterygidae)

Waage, J. K. (Division of Biological and Medical Sciences, Brown University, Providence, Rhode Island 02912) 1975. Reproductive isolation and the potential for character displacement in the damselflies, Calopteryx maculata and C. aequabilis (Odonata: Calopterygidae). Syst. Zool. 24:24-36.-Potential reproductive isolating mechanisms between sympatric Calopteryx maculata (Beauvois) and C. aequabilis Say are examined and evidence is presented for the reinforcement of species discrimination during pair formation and for a selective basis for changes in female wing pigmentation in the context of reproductive isolation between these species. The species are sympatric across the northeastern United States and southeastern Canada. In the area of sympatry C. aequabilis shows nearly complete ecological and temporal overlap with C. maculata. Mechanical barriers to interspecific copulations are apparently absent and no hybrids are known despite several observed interspecific copulations. Visual discrimination based on female wing pigmentation is identified as a major component in the reproductive isolation between C. maculata and C. aequabilis. C. maculata males discriminate between their females and C. aequabilis females by responding to the females with the darker of two alternative wing colors. Differences in wing pigmentation between sexes and among Calopteryx species are accentuated and displayed during pair formation and courtship. There is experimental evidence for the reinforcement of C. maculata male species discrimination ability in the area of sympatry with C. aequabilis. Experiments also indicate a selective disadvantage against dark winged sympatric C. aequabilis females. Coupled with the fact that sympatric C. aequabilis females have more lightly pigmented wings than allopatric ones, this finding provides a potential example of character displacement in the context of reproductive isolation between these species. [Reproductive isolation; damselflies; character displacement.] Of particular interest in the study of speciation is the origin of effective barriers to gene exchange between sympatric or parapatric populations of closely related (cognate) species. Whether these barriers result from genetic divergence during the allopatric stage of speciation, or from selection in the context of reproductive isolation during sympatry has been the subject of debate among systematists since the exchanges of Darwin and Wallace on the evolution of sterility (Dobzhansky, 1937, 1958; Fisher, 1930; Mayr, 1959). The opposing views are partially resolved (Littlejohn, 1969; Mecham, 1961) by noting that postmating incompatibility must normally arise as an incidental byproduct of divergence, either during the allopatric stage of speciation, or, less likely, during sympatry when there are sufficient restrictions to gene flow. The question then becomes: do premating isolating mechanisms also originate as incidental byproducts of divergence, or are they selected for in the context of reproductive isolation? Since these are not mutually exclusive alternatives, the question is more one of degree rather than kind. For example, a premating isolating mechanism might evolve between two species A and B in sympatry and incidentally function between one of the species and a third species C at a later time or in another part of its range (Littlejohn, 1969). The isolating mechanism would then be of incidental origin in the context of A and C or B and C, even though its origin was a consequence of selection in the context of isolation between A and B. A striking feature of the five North American Calopteryx species is the difference in wing pigmentation between sexes and among species (Howe, 1917; Walker, 1953).

Reproductive Isolation between Two Sympatric Species of Oncopeltus (Hemiptera: Lygaeidae) in the Tropics

Interspecific mating between two species of tropical milkweed bugs, Oncopeltus cingulifer Stål and O. unifasciatellus Slater, is of common occurrence in the field. However, only 0.1% of the eggs from interspecific laboratory crosses were fertile. The average duration of conspecific copulation was more than three times longer than for interspecific copulations. Since sperm transfer is slow in O. fasciatus Dallas, a closely related species, the combination of brief interspecific copulation and slow sperm transfer may result in observed infertility between O. cingulifer and O. unifasciatellus. It is suggested that interspecific matings in the field can function to maintain maximal egg production after a female mates with a conspecific.

Communal spawning of brook and river lampreys, Lampetra planeri Bloch and Lampetra fluviatilis L.

A description is given of the spawning of brook lampreys Lampetra planed Bloch and unusually small river lampreys Lampetra fluviatilis L. in the same redd. No successful interspecific copulation was observed, although the possibility of accidental cross fertilization cannot be excluded.