Mating Dynamics Research Articles

Unnatural selection: Effects of a male-focused size-selective fishery on reproductive potential of a blue crab population

A male-focused size-selective fishery, like the one targeting the blue crab ( Callinectes sapidus Rathbun) along the Atlantic and Gulf coasts of the U.S., has the potential to reduce the average size of the males in the population, reduce the density of males in the population, and/or raise the ratio of females to males. All of these may affect the mating dynamics of the population by reducing the amount of sperm that males provide to females and decreasing the number of males available for copulation. We investigated the effect of the fishery on a blue crab population in upper Chesapeake Bay by collecting crabs in areas of markedly different fishing pressure. Crabs were taken as individuals and as mating pairs, which permitted assessing the size of males currently mating in nature, and the seminal resources they possess and transfer to females. Average size of males in subpopulations that have been subjected to heavier fishing pressure is indeed smaller, and the smaller males pass less sperm and accessory fluid to females than would larger males if they were still present. Some males in pre-copulatory pairs are as sperm depleted as males that had just completed copulation, indicating that they are mating more frequently than they can replace their seminal resources. The most sperm-depleted males in the population are not even pairing or attempting to mate.

Does sex age you?

The evolution of aging and longevity has typically been considered to be a resolution of the conflicting demands on an organism to grow, reproduce, and survive. When social or environmental factors change the opportunities for reproduction in a way that affects differently aged individuals, there will be an evolutionary response in the schedule of senescence. This means that social dynamics can have an important effect on aging. A recent study by Berec and Boukal has shown that the dynamics of mating and divorce can also affect observed life spans through their effect on population dynamics. If females cannot find and maintain mating pairs for long enough to replace themselves, the population will become extinct. This puts a lower limit on the levels of longevity that will be observed in nature.

Immunomodulatory function of seminal catecholamines may be an adaptation for reproduction

Catecholamines are found at high concentrations in seminal fluid. The exact functional significance of seminal catecholamines is unknown. We hypothesize that seminal catecholamines perform important immunomodulatory functions that support reproductive success. Specifically, we propose that catecholamines contribute to a local adaptive shift of T helper (Th) balance to Th2 dominance in the maternal reproductive tract to enable the gametes, and possibly the nascent zygote, to evade immune surveillance of the female. Our hypothesis suggests that the Th2 effects of catecholamines are independent of the direct immunomodulatory effects of seminal cytokines such as prostaglandin E2 and transforming growth factor β 1. Potential immunomodulatory functions of other seminal constituents such as aldosterone, oxytocin, vasopressin, and angiotensin remain unexplored and represents a topic of future interest. Seminal stress hormones may play a role in mating dynamics since alpha males typically live in a state of high hormonal stress, Mating with adrenalized alpha males may represent an adaptive Darwinian strategy by females to maximize their reproductive fitness.

Beaks, Adaptation, and Vocal Evolution in Darwin's Finches

Abstract Darwin's finches are well known for their remarkable diversity in beak form and function. Field studies have shown that beaks evolve by natural selection in response to variation in local ecological conditions. We posit a new hypothesis: As a consequence of beak evolution, there have been changes in the structure of finch vocal signals. We base this hypothesis on the discovery that beaks play a functional role in song production in songbirds. Recent field studies provide support for a link between beak morphology and song structure in Darwin's finches, although much remains to be learned. Because song plays a significant role in finch mating dynamics, we suggest that the functional link between beaks and song may have contributed to the process of speciation and adaptive radiation in these birds.

Experimental demonstration that pre- and post-conceptional mechanisms influence sex ratio in mouse embryos.

Previously we have demonstrated in two monotocous species (bovine and sheep), a relationship between time of insemination, moment of ovulation, and embryo sex ratio. Here, we have analyzed in a polytocous specie (mice) if in addition to pre-conceptional mechanisms, also post-conceptional ones affect the offspring sex ratio. To verify this hypothesis we carried out two experiments. In the first experiment, we analyzed the effect of mating dynamics on the sex ratio of mice with synchronic male and female embryo development. Females were mated before and after ovulation and sacrificed 13 days later for sex determination of embryos and reabsorptions. A decreased litter size, and an increased offspring sex ratio in matings occurring later in oestrus, supported the view that a biased sex ratio may occur as the result of behavioral differences between the populations of X- or Y-bearing spermatozoa. In the second experiment, embryos developmentally synchronic and asynchronic with the recipient female endometrium were transferred, and again, 13 days later, females were sacrificed for sex determination of embryos and reabsorptions. The male proportion per litter found, indicated that our developmentally asynchronic transfers favored a sex ratio disbalance at birth. When combined, these results become the first experimental evidence supporting the view that both pre- and post-conceptional mechanisms of sex ratio distortion in polytocous species are not mutually exclusive and both may explain, under different conditions, sex ratio deviations at birth.

Evaluation of mating dynamics in a lodgepole pine seed orchard using chloroplast DNA markers

Chloroplast DNA (cpDNA) markers were used to evaluate pollen dynamics in an operational lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seed orchard. High levels of cpDNA differentiation were obtained using six primer pairs specific to simple sequence repeat (SSR) and variable number tandem repeat (VNTR) loci dispersed around the lodgepole pine chloroplast genome. In 69 orchard parents genotypes, 46 multilocus haplotypes were detected with 31 of these being unique (i.e., having only one orchard parent). The number of variants (alleles) per locus ranged from two to seven with gene diversity levels of 0.44-0.72. Evaluation of wind-pollinated seedlots of 15 selected clones using these markers indicated low levels of selfing (2%) and pollen contamination (5%) but showed evidence of relatively high levels of differential male reproductive success.

Trade-offs, the allocation of reproductive effort, and the evolutionary psychology of human mating

This response reinforces several major themes in our target article: (a) the importance of sex-specific, within-sex variation in mating tactics; (b) the relevance of optimality thinking to understanding that variation; (c) the significance of special design for reconstructing evolutionary history; (d) the replicated findings that women's mating preferences vary across their menstrual cycle in ways revealing special design; and (e) the importance of applying market phenomena to understand the complex dynamics of mating. We also elaborate on three points: (1) Men who have indicators of genetic fitness may provide more direct benefits when female demand for extra-pair and short-term sex is very low; (2) both men and women track ecological cues to make mating decisions; and (3) more research on female orgasm is needed.

Regiospecificity of nucleotide-amino acid mating vs. water dynamics: a key to protein-nucleic acid assemblies: structure of unidecahydrated inosine-5'-monophosphate and L-glutamic acid (2C10H13N4O8P.C5H11NO4.11H2O) cocrystal at atomic resolution

The crystal structure of a unidecahydrated cocomplex between two Inosine-5′-monophosphates (IMP) and one L-glutamic acid has been determined by X-ray crystallographic methods. The crystal belongs to the monoclinic space group P21 with cell dimensions a = 8.650(1), b = 21.900(1), c = 12.370(1) A, and β = 110.4°(9). This structure reveals extensive hydrogen bonding of glutamic acid to the nucleotide through direct and water-mediated interactions. The phosphate oxygens (O3B and O1B) seem to prefer nonspecific interaction with the functional sites of glutamic acid (OE2 ······O1B = 1.78 A, NA······O3B = 2.73 A, OH······O3B = 3.06 A), whereas the bases prefer specific (O······N3B = 2.88 A) binding. A solvent mediated N7A···W5···N7B hydrogen bond used for stabilization of the stacked purine bases has been observed as in other amino acid–nucleotide cocrystals. Glutamic acid occupies the same hydrophilic region in the nucleotide cocrystal as was found in glutamine–inosine monophosphate (Gln–IMP) and in serine–inosine monophosphate (Ser–IMP) complexes through substantial replacement of free and bound water molecules. This points to the dynamic hydrogen bonding nature of the water molecules and their stereochemical cooperation for the placement of amino acid through the polycoordination within the crystal.

Resource presence and operational sex ratio as determinants of copulation duration in the flyRhagoletis juglandis

The effects of the interaction between the operational sex ratio (OSR) and a resource (i.e. oviposition site) on mating dynamics have rarely been considered. We examined the effect of the resource presence and its interaction, with the effect of OSR on copulation duration inRhagoletis juglandis, a tephritid fly species characterized by a resource-defence mating system in which males defend territories on walnut fruit. In this species, copulation duration varies from 30s to over 1h and was shown previously to respond strongly to changes in OSR. In the field, short copulations tended to begin and end on fruit, whereas most long copulations generally began on fruit but ended in the foliage, suggesting a possible effect of resource presence on the copulation duration. In laboratory assays of isolated pairs, copulations were significantly shorter in the presence of a surrogate fruit, confirming the effect of resource presence. In another laboratory assay, in which we manipulated OSR independently of resource presence, resource presence and OSR were additive in their effects. Results are discussed in the context of sperm competition theory.

Multiple choice criteria and the dynamics of assortative mating during the first breeding season of female snow crab Chionoecetes opilio (Brachyura, Majidae)

Crab pairs, consisting of a male grasping another crab (the graspee), were collected by divers during the first breeding season of female snow crab Chionoecetes opilio. Different types of graspees were found and were ranked according to their reproductive value to the male. High-value graspees were pubescent females (close to their terminal maturity molt) and nulliparous females (just molted and close to oviposition). Postmolt primiparous females (clean-soft shell and carrying eggs) also mated and were inseminated by males, but they were of less value than pubescent or nulliparous females as there was only a remote chance that the males' stored sperm would be used to fertilize the next egg clutch. Females copulated with up to 6 different males during their first breeding season. Another category of graspees including males and juvenile females provided the grasping male with no fecundity benefit. Pubescent females paired with males up to 13 d before molting. Males grasping the high-value pubescent and nulliparous females were larger, had a harder shell, and were missing fewer limbs than the males grasping low-value primiparous females, other males or juvenile females and than the overall population of adult males on the mating grounds assessed by trawl. Size-assortative mating by male chela size and female carapace width occurred in the predominant pubescent pairs. Moreover, males with larger chelae were associated with pubescent females missing fewer limbs or having relatively narrower abdomens. Both traits may influence female survivorship and lifetime fecundity. The complex assortative mating pattern of snow crabs apparently derives from mate choice and male sexual competition in the context of prolonged attractiveness of pubescent females to males.

Application of a chloroplast DNA marker in seed orchard management evaluations of Douglas-fir

We evaluated pollen contamination, supplemental mass pollination efficacies, and natural selfing in a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) clonal-row seed orchard using a genetic marker on the paternally inherited chloroplast (cp) genome. A primer pair for the polymerase chain reaction amplification of a variable region on the cpDNA in Douglas-fir was developed. The amplified DNA product was highly variable in size, yielding 13 different haplotype bands from 20 orchard genotypes growing in the clonal-row seed orchard. Observed band sizes ranged from 859 to 1110 base pairs (bp). To estimate variation levels in the orchard background pollen pool, 96 assayed genotypes from surrounding stands gave rise to 36 different haplotypes, ranging from 367 to 1119 bp in size, resulting in a gene diversity estimate of 0.91. Most orchard clones' haplotypes were also present in the background. After adjusting for the presence of orchard-type haplotypes in the background, contamination was found to be 40%. Natural selfing in six individual clones ranged from 0 to 19% with an average of 6%. Supplemental mass pollination efficacy was estimated to be 55%, ranging from 39 to 73%, depending on the maternal clone and flowering phenology. This DNA marker proved to be very useful in assessing seed orchard mating dynamics and orchard management efficacies for Douglas-fir.

Timing of Mating, Developmental Asynchrony and the Sex Ratio in Mice

Krackow, S. and P. S. Burgoyne. Timing of mating, developmental asynchrony and the sex ratio in mice. PHYSIOL BEHAV 63(1): 81–84, 1998.—According to the developmental asynchrony hypothesis, changing the time of mating within the estrous cycle could alter the interval between completion of blastocyst development and uterine responsiveness for implantation. This may then lead to sex ratio skews in animals that exhibit sex-differential blastocyst development, because uterine stage may now benefit either slow (female) or fast (male) developing blastocysts. To test this hypothesis, the responses of two strains of mice to altered mating dynamics were compared. In a strain that exhibits higher male than female blastocyst developmental rates, sex ratios became significantly female-biased when mated late during the estrous cycle as opposed to early mating. However, timing of mating did not affect sex ratios in a strain with synchronous development of male and female preimplantation embryos. Hence, it is concluded that developmental asynchrony between male and female blastocysts on the one hand, and blastocysts and uterus on the other, are indeed responsible for the effect of timing of mating on litter sex ratios in mice.

Effects of mating dynamics and crowding on sex ratio variance in mice.

Mating units of six virgin females and one adult stud male were established to test for the effects of timing of mating and crowding of pregnant females on litter sex ratios in mice. Females either copulated during periods when no other female of the mating unit copulated simultaneously (single mating condition) or when more than one female copulated (multiple matings condition). Two crowding conditions were imposed on the animals: the females of 14 mating units were placed into individual cages after mating (isolated condition), while females of the other 13 mating units remained in the original group until shortly before littering (crowded condition). Sex ratio variance did not deviate from random expectation in litters arising from the multiple matings periods. However, in litters arising from single mating periods, extreme sex ratios were found significantly less frequently than expected by chance. Higher sex ratio variance in litters arising from multiple matings periods is attributed to the timing of mating being at higher variance under this condition, which is known to affect sex ratios in other rodents. Crowding significantly reduced sex ratio variance further. Reduced sex ratio variance under single mating and crowded conditions is speculated to follow from competition for resources between preimplantation embryos, which may be further increased by stressful effects of crowding. Loss of embryos after implantation appeared not to be responsible for the above effects.

Attributes of oviposition substrates affect fecundity in Rhodnius prolixus

The effect of the oviposition substrate on the rate of egg laying was investigated in the haematophagous bug Rhodnius prolixus. Fresh or old hen feathers or corrugated cardboard were offered to ovipositing females. The insects showed significant differences in the number of eggs laid depending on the substrate. Egg laying was maximal on the fresh feathers and minimal on the cardboard. The variations cannot be explained by differences in the amount of blood ingested nor by differences in the mating frequency between treatments. The amount of blood necessary per laid egg exhibited an inverse relationship with the absolute fecundity. The dynamics of mating and egg-laying for groups having two different substrates (corrugated cardboard and hen feather) and different nutritional states (previously starved vs previously fed) was established throughout one month. After a single meal, previously starved insects having feathers as a substrate laid their eggs and reached an oviposition peak sooner (6 days) than previously starved insects on the cardboard substrate. For both nutritional states the lack of feathers decreased the cumulative number of eggs laid by one third. Results are discussed in relation to the mechanisms of ovarian regulation known at present.

Direct and indirect effects of multiple enemies on water strider mating dynamics

Previous studies have shown that green sunfish, Lepomis cyanellus, have strong effects on the activity, habitat use, social interactions and mating dynamics of a stream-dwelling water strider, Aquarius remigis (family Gerridae, hence, gerrids). In nature, however, stream pools often contain not just sunfish and water striders, but also smaller fish such as minnows. Here, we used factorial experiments in seminatural streams to document the direct and indirect effects of sunfish and fathead minnows, Pimephales promelas, on water strider survival and behavior. Sunfish, minnows and gerrids all consume surface prey (here, crickets); thus these three species are potential food competitors. Sunfish eat minnows. Accordingly, the presence of sunfish caused minnows to increase their schooling behavior and shift their activity from the surface toward the bottom substrate. The presence of sunfish was also associated with an increase in the number of missing gerrids, whereas minnows caused relatively little gerrid disappearance. Most interestingly, the presence of minnows decreased the effect of sunfish on gerrid disappearance rates; that is, minnows apparently had an indirect positive effect on water strider survival. We suggest that this indirect positive effect reflects the fact that minnows are alternative prey for sunfish. The effects of sunfish and minnows on gerrid mortality explained the influence of these fish on gerrid behavior. Sunfish caused decreases in male gerrid activity, female availability, mating activity, mating frequency and mating duration. Larger males had a mating advantage over smaller males only in pools with sunfish and no minnows. Sunfish also caused a borderline significant decrease in the large female mating advantage. These results were all observed in previous studies and can be viewed as adaptive responses to predation risk. These patterns were not consistent with the expected effects of sunfish as food competitors with water striders. In contrast, minnows had relatively little influence on water strider behavior and the few significant effects were the opposite of those of sunfish. Minnows caused increases in female activity and in mating duration, a decrease in the large male mating advantage and an increase in the large female mating advantage. These patterns fit the view that minnows caused an increase in gerrid hunger, i.e., that minnows acted as food competitors with gerrids. Finally, planned contrasts against controls showed that, in the presence of both sunfish and minnows, water striders showed no significant behavioral responses to fish (i.e., gerrid behavior in pools with sunfish and minnows did not significantly differ from behavior in fishless pools). The most likely mechanism explaining this pattern is a dilution of sunfish predation risk due to the presence of minnows serving as alternative prey for sunfish.

An experimental test of condition-dependent mating behavior and habitat choice by water striders in the wild

Individual condition is expected to be an important determinant of many behaviors, including mating dynamics and habitat choice. In this study we experimentally investigated the linkages between individual condition, habitat use, and mating dynamics in the wild. We manipulated recent feeding history of the water strider, Aquarius remigis, and then quantified the habitat use and mating activity of males and females. Females could choose from three habitats (refuge, near shore, and open). On the water surface (open and near-shore habitats), in contrast to refuge, females can forage, but they are exposed to predation and sexual harassment by males. We tested three main hypotheses. First, we predicted that single females that were fed, relative to those that were not, would reduce their exposure to predators and male harassment by increasing their use of refuge. Similarly, we predicted that fed females that were mating would spend more time in refuge than those that were not fed. Our results support these two predictions. Fed single and mating females significantly increased their use of refuge. Third, we predicted that mating activity (proportion of time spent mating) of fed females would be reduced relative to starved females, because of reduced exposure to males while in refuge, and perhaps because of decreased receptivity to male mating attempts while on the water surface. Mating activity of fed females was about one third that of starved females. The decrease in mating activity could not be accounted for by any change in female receptivity, but could be accounted for by change in habitat use. The decrease in mating activity may have resulted from decreases in both mating frequency and mating duration. Our estimates of minimum mating frequency indicate a large and significant decrease, but we were unable to assess mating duration. We found no significant effect of our manipulation on habitat use or mating activity of males.[Behav Ecol 7: 474–479 (1996)]

How Likely Is Male Mate Choice Among Anurans?

Male mate choice has received considerable attention in recent years. This phenomenon rarely has been demonstrated in anuran mating systems, nonetheless, male choice has been suggested as having a significant impact on some anuran pairing patterns. Here I present a quantitative model that predicts the potential and prevalence of male mate choice in nine anuran species with data available in the literature. Males of only four of the nine species (Bufo americanus, B. bufo, B. exsul, and Rana sylvatica) are predicted to reject females under Normal conditions; in those cases only the smallest 1% to 5% of the females, respectively, should be rejected. By contrast, male Bufo conorus, B. cognatus, Hyla rosenbergi, Physalaemus pustulosus, and Rana catesbeiana are not expected to reject females of any size. Not until operational sex ratios became lm: lf and search times were reduced to 30%, on average, of normal values will reject and accept strategies become equally prevalent. Thus for these nine anuran species, the quantitative model presented here elucidates why the extent of male mate choice may be very limited, and why it is not expected to exert a strong influence on mating dynamics or pairing patterns.

Interacting effects of predation risk and male and female density on male/female conflicts and mating dynamics of stream water striders

Interacting effects of predation risk and male and female density on male/female conflicts and mating dynamics of stream water striders

Predation risk and the evolutionary ecology of reproductive behaviour

A large literature exists on the effects of predation risk on foraging and survival‐related behaviours. In contrast, with some notable exceptions, relatively few theoretical or experimental studies have examined the effects of predation risk on reproductive behaviours. Existing literature on risk and reproductive behaviour and suggestion directions for future study are reviewed. In particular: (1) effects on predation risk on mating behaviour; (2) the influence of spatial patchiness on interactions between risk and reproductive behaviour; (3) the potential influence of multi‐species interactions on the effects of predation risk on mating dynamics; (4) the importance of looking at sets of inter‐related antipredator traits; and (5) some effects of predation risk on prey population patterns due to changes in prey reproductive behaviour are discussed. To illustrate various points examples involving fish and other aquatic organisms are used.

Helpers liberate female fairy-wrens from constraints on extra-pair mate choice

In cooperatively breeding superb fairy-wrens (Malurus cyaneus), all males contribute to the feeding and defence of young. Despite the expectation that such paternal care should be directed only to relatives, DNA fingerprinting revealed that most offspring (76%, 138 out of 181) were sired by extra-group males that contributed no care, and that almost all broods (95%, 38 out of 40) contained young sired by extra-group fathers. This is the highest known incidence of cuckoldry. This remarkable mating system is produced by female control of fertilization and consistent preference for certain extra-group male genotypes. This choice leads to the production of sons that also gain extra-group fertilizations. One constraint on the extra-pair mate choice of females is the level of parental assistance received from males. Males living in pairs contribute relatively more parental care and are more likely to gain paternity in one of their broods (85%, 11 out of 13) than dominant males in multi-male cooperative groups (30%, 8 out of 27). In groups helpers compensate for the lower parental assistance of dominant males, so the total feeding rate is similar between pairs and groups. This suggests that females allow males in pairs more paternity to ensure their assistance with parental care. Helpers provide an alternative source of paternal investment, and allow females to express unrestricted mate choice. Mating options for females in other species with female control of fertilization may also reflect a trade-off between acquiring the genes of high-quality males for their offspring and parental care of those offspring.