Unpaired Males Research Articles

Intrasexual mounting in the beetle Diaprepes abbreviatus (L.).

The weevil Diaprepes abbreviatus shows three kinds of same-sex mountings: males mount other unpaired males, males mount males already engaged in copulation and females mount other females. Four hypotheses were evaluated in order to explain same-sex matings by males: (i) female mimicry by inferior males, (ii) dominance of larger males which affects the behaviour of small males, (iii) sperm transfer in which smaller males gain some reproductive success by 'hitchhiking' their sperm with the sperm of larger males, and (iv) poor sex recognition. Data from mate choice and sperm competition experiments rejected the female mimicry, dominance and sperm transfer hypotheses and supported the poor sex recognition hypothesis. We tested three hypotheses in order to explain female mounting behaviour: (i) females mimic male behaviour in order to reduce sexual harassment by males, (ii) females mount other females in order to appear larger and thereby attract more and larger males for mating, and (iii) female mimicry of males. The results of our mate choice experiments suggested that the female mimicry of males hypothesis best explains the observed female mounting behaviour. This result is also consistent with the poor sex recognition hypothesis which is the most likely explanation for male and female intrasexual mating behaviour in many insect species.

Aggregating Behavior During Oviposition in the Dragonfly Sympetrum vicinum (Hagen) (Odonata: Libellulidae)

Abstract This study examined the adaptive significance of ovipositing near conspecifics by pairs of the dragonfly Sympetrum vicinum. Studies were conducted at two artificial ponds in New York using a series of 1 m2 plots along their shorelines. Although the majority of pairs oviposited alone, pairs also tolerated the presence of others only 5–10 cm away, and sometimes 2–7 pairs oviposited together within a single plot. Habitat selection (preference for certain plots over others) partially accounted for such behavior. However, where adjoining plots were homogeneous (i.e., used equally for oviposition), newly arriving pairs were more likely to begin dipping in a plot in which one or more pairs were already present, thus also suggesting mutual attraction among pairs. Oviposition efficiency (measured as no. abdominal dips/s) was apparently not compromised by ovipositing near conspecifics. Harassment from unpaired males had little effect on oviposition since unpaired males were uncommon and rarely approached p...

Song, sexual selection, and a song control nucleus (HVc) in the brains of European sedge warblers

Female sedge warblers select males that have more complex songs as mates. This study tests two predictions concerning HVc, a telencephalic nucleus that is essential for song learning and production: first, that males with more complex songs will have a larger HVc, and second that males who pair successfully will have a larger HVc than unpaired males. Data on song composition and pairing status were collected from wild sedge warblers breeding in Hungary. We found significant positive correlations between three song attributes (repertoire size, song complexity, and song length) and the size of HVc. Males that paired successfully also had more complex songs (repertoire size and song complexity, though not song length) than males that did not. However, we find no direct evidence that males who paired successfully had a larger HVc than unpaired males. These findings are discussed in relation to the possible functions of HVc and also to current views on sexual selection and the evolution of the song control pathway. © 2000 John Wiley & Sons, Inc. J Neurobiol 44: 1–6, 2000

The role of behavioural ecology of damselflies in the use of fluctuating asymmetry as a bioindicator of water pollution

Summary1. Fluctuating asymmetry has been used widely to investigate questions concerned with evolution and behaviour, and to study the effects of environmental pollution. Damselflies have been used to answer questions in both fields, but no attempt has been made to combine the knowledge from these areas to investigate whether and how evolutionary ecology and behaviour interfere with the use of fluctuating asymmetry as a bioindicator of water pollution.2. Four hypotheses were formulated to investigate possible interferences: (1) Paired males should be less asymmetrical than unpaired males. (2) Males caught at breeding sites should be less asymmetrical than females caught at breeding sites. (3) Damselflies caught earlier in the season should be less asymmetrical than those caught later in the year. (4) Damselflies caught at control sites should be less asymmetrical than those caught at sites within areas of high pesticide usage.3. No significant difference in asymmetry levels was found between paired and unpaired males.4. Males were significantly less asymmetrical than females.5. Damselflies caught earlier in the year were less asymmetrical than those caught later.6. The data used to test the hypothesis that fluctuating asymmetry in the wings of mature damselflies reflects the level of pesticides used in the surrounding environment were equivocal.7. The findings suggest that evolutionary ecology and behaviour interfere with the suitability of fluctuating asymmetry in mature damselflies as a biomonitoring tool and it is concluded that fluctuating asymmetry in emerging adults should be much more appropriate as a bioindicator.

Survival, Emigration, and Winter Population Structure of Harlequin Ducks

AbstractA population of individually marked Harlequin Ducks (Histrionicus histrionicus) at White Rock, British Columbia, Canada was examined to measure the degree of population differentiation among birds which pair during the winter months. This required an understanding of the patterns of emigration among wintering sites in different segments of the population. Some juveniles arrived at the wintering grounds accompanied by their mothers, thus initially arriving into the same winter population as their parents. Young males were more likely than young females to disperse during the first two years of life. Adult males had higher local survival than adult females during the summer months, probably because of the greater mortality risks to nesting females. During the nonbreeding seasons, local survival was the same in both sexes. Paired males had a local survival of more than 90%, suggesting both high survival and strong philopatry. Unpaired males had a lower local survival rate, suggesting they have higher mortality and/or emigration rates. Young females had the same local survival rate as adult females, suggesting that they did not disperse during the winter. These winter philopatry patterns are similar to the general pattern of breeding philopatry in waterfowl, with females showing stronger philopatry than males, and paired adults stronger philopatry than unpaired and young birds. The dispersal of young males makes local population differentiation unlikely in this species.

Song, sexual selection, and a song control nucleus (HVc) in the brains of European sedge warblers

Female sedge warblers select males that have more complex songs as mates. This study tests two predictions concerning HVc, a telencephalic nucleus that is essential for song learning and production: first, that males with more complex songs will have a larger HVc, and second that males who pair successfully will have a larger HVc than unpaired males. Data on song composition and pairing status were collected from wild sedge warblers breeding in Hungary. We found significant positive correlations between three song attributes (repertoire size, song complexity, and song length) and the size of HVc. Males that paired successfully also had more complex songs (repertoire size and song complexity, though not song length) than males that did not. However, we find no direct evidence that males who paired successfully had a larger HVc than unpaired males. These findings are discussed in relation to the possible functions of HVc and also to current views on sexual selection and the evolution of the song control pathway.

SURVIVAL, EMIGRATION, AND WINTER POPULATION STRUCTURE OF HARLEQUIN DUCKS

Abstract A population of individually marked Harlequin Ducks (Histrionicus histrionicus) at White Rock, British Columbia, Canada was examined to measure the degree of population differentiation among birds which pair during the winter months. This required an understanding of the patterns of emigration among wintering sites in different segments of the population. Some juveniles arrived at the wintering grounds accompanied by their mothers, thus initially arriving into the same winter population as their parents. Young males were more likely than young females to disperse during the first two years of life. Adult males had higher local survival than adult females during the summer months, probably because of the greater mortality risks to nesting females. During the nonbreeding seasons, local survival was the same in both sexes. Paired males had a local survival of more than 90%, suggesting both high survival and strong philopatry. Unpaired males had a lower local survival rate, suggesting they have highe...

Postcopulatory Behavior in Libellula pulchella Drury (Odonata: Libellulidae) and Female Tactics for Avoiding Male Interference with Oviposition

Postcopulatory behavior was studied in Libellula pulchella, a North American dragonfly in which ovipositing females face frequent harassment by unpaired males seeking matings. Although males performed noncontact guarding of their mates after copulation, females received minimal protection since their guarders tended to leave on extended chases of other males when harassment was intense. Ovipositions by unguarded females were even more likely to be terminated by harassment and were disrupted sooner. Female tactics to minimize interference included rapid escape flights, repeated return visits to the water within short time periods, perching when severerly harassed, and proceeding with mating when clasped. Female use of multiple oviposition sites is discussed in the context of guarding effectiveness and mate recognition by males.

Wing length and asymmetry of male Tokunagayusurika akamusi chironomid midges using alternative mating tactics

Male Tokunagayusurika akamusi chironomids have alternative mating tactics. One is to search for females on vegetation (ground mating), and the other is to wait for females in an aerial swarm (swarm mating). Simultaneous sampling of ground-unpaired and ground-paired males and of swarm-unpaired and swarm-paired males were performed. The average wing length and right-left wing length difference (wing asymmetry) were compared between males from the four different categories. Swarm-unpaired males were larger than ground-unpaired ones, swarm-paired males were larger than swarm-unpaired ones, and ground-paired males were not larger than ground-unpaired ones. Thus, large males tended to aggregate in swarms, and larger swarming males mated more successfully. On the other hand, small males probably enjoyed mating on the ground, especially when large males swarmed. The wing asymmetry was not significantly different between unpaired and paired males both within and between tactics. There was a flat or U-shaped relationship between wing length and asymmetry, underpinning the lack of a symmetrical advantage of swarming to large males. The right-left difference was not normally distributed in four of six samples of unpaired males but, in contrast, was not normally distributed in only one of six samples of paired males. The non-normal distributions were leptokurtic and included outliers. Removal of the outliers improved normality, suggesting that males with extremely asymmetric wings were not successful in mating.

Floater males gain reproductive success through extrapair fertilizations in the stitchbird

We used minisatellite DNA profiling to assign parentage to stitchbird, Notiomystis cincta, chicks from a breeding population on Tiritiri Matangi Island off the coast of the North Island of New Zealand. The small population size allowed samples to be collected from all potential parents and nearly (33/34 nestlings) complete assignment of paternity. Analysis revealed that 35% of nestlings (12/34) were the result of extrapair copulation and that extrapair young were present in 80% of nests (8/10). About half of the extrapair nestlings were the offspring of unpaired males. This is substantially higher than predicted from the literature, which suggests that extrapair paternity is typically gained by paired males.

Seasonal Patterns of Sex Steroids Determined from Feces in Different Social Categories of Greylag Geese (Anser anser)

Seasonal patterns of fecal 17β-OH-androgen, estrogen, and progesterone equivalents of male and female greylag geese (Anser anser) were analyzed in a flock of free-living geese. These were compared among social categories determined by pairbond status and breeding success. The annual cycle was divided into 13 phases. Phasewise intra-sexual comparisons were made between social categories. The seasonal variation obtained from feces was in general agreement with the literature on plasma patterns in geese and other temperate-zone birds. However, there were distinct differences in seasonal hormone patterns among the social categories. In unpaired males, androgen was elevated for a longer period of time during sexually active phases compared with paired males. In male geese, high levels of androgen did not interfere with parenting but were related to pairbond status, whereas in females, androgen and progesterone were positively related to parental behavior. In the Fall, androgen, progesterone, and estrogen peaked only in unpaired males. In unsuccessful females, estrogen started to increase earlier in the Winter and was higher in amplitude and duration than that in females guarding offspring. In general, fecal steroids showed a clear-cut difference only between sexually active and parental phases of the year in the successfully breeding pairs, whereas unpaired males retained a hormonal state closer to sexually active phases throughout the year.

Assortative pairing with respect to parasite load in the beetle Timarcha maritima (Chrysomelidae)

Abstract Because of their effects on host reproductive behaviour, parasites are theoretically expected to create sometimes assortative mating among hosts, with heavily parasitized individuals pairing together and lightly parasitized ones pairing among themselves. We investigated the influence of protozoan gut parasites on the pairing pattern of the chrysomelid beetle Timarcha maritima. In the field, fecundity was negatively correlated with the parasite load of females, unpaired males were significantly more heavily infected than paired ones and, among pairs, males and females were matched for parasite load. Mate choice experiments in the laboratory showed that males have some ability to avoid heavily infected partners when given the choice between two females. Male competitiveness, measured as their mobility, was also negatively correlated with parasite load. These results indicate that parasite-related assortative pairing in this beetle could result from parasitized females being less fecund and parasitized males less competitive.

Pairing success relative to male plumage redness and pigment symmetry in the house finch: temporal and geographic constancy

Male house finches (Carpodacus mexicanus) have carotenoid-based ornamental plumage coloration. In previous research it was shown that for a single population of house finches in a single year, males that paired were on average redder in plumage coloration than males that did not pair, and males with redder plumage tended to nest earlier than males with less red plumage. Here we show that these patterns continued over 6 years and at two widely separated locations. We also tested whether the symmetry of carotenoid-based crown pigmentation differed between paired and unpaired males and found that paired males have, on average, more perfect symmetry of crown pigmentation than males not paired. These observations support the idea that expression of carotenoid-based plumage coloration by males is a persistent and widespread criterion in female mate choice in the house finch.

Costs and benefits for water strider (Aquarius paludum) females of carrying guarding, reproductive males

We describe the mating system of Aquarius paludum insularis based on field observations and test hypotheses about the effects of body size, hunger level and post‐copulatory guarding on reproductive performance. The mating sequence of this species was typical for temperate water striders, except that most oviposition was carried out by tandem pairs, most of which were submerged. Mate guarding continued until the end of oviposition, lasting up to 18.2 h, which was much longer than that recorded for other species of water striders. Pair partners changed after oviposition. Extended contact guarding reduced female mobility. In the case of females that carried long‐winged males, there was a significant reduction in speed and stride between tandem as opposed to single females. However, when short‐winged males were carried, there was not a significant difference. Short‐term foraging efficiency did not differ significantly between tandem and single females, and thus did not reflect the difference in mobility. Hunger level did not significantly affect female mating receptivity. Although the number of harassment bouts by unpaired males did not differ between single and tandem females, single females suffered significantly more harassment. Females were able to lay fertilized eggs for about 15 days after a single copulation, but they accepted long guarding and multiple mating during this period as well. The cost of resisting male mating attempts appears to be greater than the cost of carrying males.

Correlates of reproductive success in a population of nine-banded armadillos

We used microsatellite DNA markers to identify the putative parents of 69 litters of nine-banded armadillos (Dasypus novemcinctus) over 4 years. Male and female parents did not differ in any measure of body size in comparisons with nonparents. However, males observed paired with a female were significantly larger than unpaired males, although paired females were the same size as unpaired females. Females categorized as possibly lactating were significantly larger than females that were either definitely lactating or definitely not lactating. There was no evidence of assortative mating: body-size measurements of mothers were not significantly correlated with those of fathers. Nine-banded armadillos give birth to litters of genetically identical quadruplets. Mothers (but not fathers) of female litters were significantly larger than mothers of male litters, and maternal (but not paternal) body size was positively correlated with the number of surviving young within years, but not cumulatively. There were no differences in dates of birth between male and female litters, nor were there any significant relationships between birth date and maternal body size. Body size of either parent was not correlated with the body sizes of their offspring. Cumulative and yearly reproductive success did not differ between reproductively successful males and females. Average reproductive success (which included apparently unsuccessful individuals) also did not differ between males and females. The majority of adults in the population apparently failed to produce any surviving offspring, and even those that did usually did so in only 1 of the 4 years. This low reproductive success is unexpected, given the rapid and successful range extension of this species throughout the southeastern United States in this century.

Variable Social Mating System in the Sedge Warbler, Acrocephalus schoenobaenus

AbstractWe studied the mating system in a local population of colour‐ringed sedge warblers in south Central Sweden in 1990–92. Of 58 territorial males, 59% were socially monogamous, 14% socially polygynous and 27% unpaired. Socially polygynous males in general paired with two females: the only exception was one male that formed pair bonds with three females. Among the males that formed a pair bond, 38% resumed singing after their first female had started egg‐laying or incubation and 50% of the paired males that resumed singing succeeded in attracting a second female. Hence, despite a consistently male‐biased sex ratio in the population a large proportion of the males tried to become polygynous and they were often successful. The frequency of extra‐pair matings did not differ between monogamous and polygynous males. Of 47 breeding females, 6.4% were sequentially socially polyandrous. In two out of three cases, the females fed the young of their first broods until independence before initiating the second brood. In the third case the female deserted her newly fledged young and these were instead cared for by a neighbouring male. DNA fingerprinting revealed that this male had not sired any of these young. Each of the sequentially polyandrous females successfully raised both their broods, and their annual reproductive success was slightly higher than the average for the polygynous males. When the sequentially socially polyandrous females initiated their second brood, their primary male (in all cases polygynous males), cared for young in their secondary female's nest. In all cases, the sequentially polyandrous females formed second pair bonds with unpaired males that were close neighbors. This suggests that females switched pair male for their second brood to obtain a mate that was more likely to provide them with direct benefits (e.g. parental care).

Spring home range and social behavior of Hazel grouse at Changbai Mountain

The spring home range and social behavior of Hazel grouse, (Bonasa bonasia) were studied at Changbai Mountain using radiotelemetry in 1993–94. Flock dissolution and pair formation started in mid-March. Paired males held territories in spring, the area was from 3.2 hm2 to 17.3 hm2 (n=2). Hazel grouse was proved to be monogamous by radiotelemetry work. The overlap of home range between paired No.10 and No.8 was 82.4%. The time of birds being together was 83.0% of the time during the prelaying period (n=53), showing that the pair bond was stable. Unpaired males showed different behavior, held a territory or wandering, and they changed their behavior in early May. The study suggested that unpaired males gave up their reproduction goal, and the acquisition for survival became more important in early May, when female started incubation.

Song structure in the Hoopoe (Upupa epops) — Strophe length reflects male condition

The structure of Hoopoe (Upupa epops) song is analysed in a colour ringed population in southern Spain. The song of males in this species is very simple, with a repertoire size of one. The strophes of a male only differ in the number of elements that they include (strophe length), and strophe length is the main song feature differing between males. During the prelaying period each individual used mainly strophes of only two lengths, between 2 and 6 elements per strophe, and mean strophe length of males during this period was highly repeatable. However, some males changed the range of strophe types produced and decreased their mean strophe length after unsuccessful breeding or spending long periods of time singing (unpaired males). These changes show that strophe length is phenotypically plastic, and suggest that singing long strophes is energetically more costly than singing short ones. The significant relationship between strophe length and body condition, and the fact that long strophes were associated with longer previous pauses than short strophes, also suggest that increasing strophe length is costly. All these findings are in accordance with the hypothesis that strophe length reflects male condition in the Hoopoe, although it is not clear what the actual cost of singing long strophes is.

Distribution and reproductive success of the Pied Flycatcher Ficedula hypoleuca in relation to forest patch size and vegetation characteristics; the effect of scale

We studied habitat choice, distribution and reproductive success in the Pied Flycatcher Ficedula hypoleuca in relation to the spatial structure of a fragmented forest area. Two hierarchical levels of forest habitat structure were used: (1) forest patch size (macrohabitat) and (2) vegetative structure within forest patches (microhabitat). In spring, both males and females settled preferentially in large and medium‐sized forest stands (>1 ha) where breeding density was also higher than in small stands (<1 ha). Stands <5 ha were occupied later, and the proportion of unpaired males was higher there than in large stands (>5 ha). The known age distributions of breeding birds and breeding success were independent of forest patch size. Nest predation rate was not associated with stand size or nest distance from the forest edge. The preference of breeding birds for large forest patches was presumably related to the higher amount of resources (nest sites, mates, food) a large patch can offer for reproduction compared with a small patch. At the microhabitat level, territories of old males were characterized by relatively more deciduous trees that contained more invertebrate food than coniferous tree‐dominated territories of yearling males. The reproductive success of old males, as measured by the number of fledged young per male, was higher than that of yearling males. This suggests that the larger body size and blacker plumage of old males possibly contributed to male dominance and that old males excluded younger males from preferred habitats through territorial behaviour. Our results suggest that habitat choice of the Pied Flycatcher was affected by both micro‐ and macrohabitat. On the basis of settlement pattern, density and reproductive success, the distribution of Pied Flycatchers across forest stands of different sizes followed the ideal‐free distribution model, whereas at the microhabitat level, age‐related unequal distribution of males followed the ideal‐despotic model of Fretwell and Lucas.

A finite time horizon influences sequential mate choice in male Gammarus aequicauda (Amphipoda)

Although size-assortative pairing has been extensively studied in amphipods, the influence of time left to moult (TLM) on pairing decisions of male gammarids remains largely unexplored. Given that moulting males cannot guard their mates, we investigated the influence of TLM for males on size-assortative mating in the gammarid Gammarus aequicauda (Crustacea, Amphipoda). There was a significant relationship between TLM and size in males. Unpaired males were closer to their moult than paired ones. Among pairs, there was a significant positive relationship between male and female sizes and between male and female TLM values. However, males closer to the moult were paired with females of more varying sizes than were other males, suggesting that a decrease in TLM reduces choosiness in males. Although there was a significant relationship between TLM and size in males, size-assortative mating was independent of male TLM.