Alternative mating tactics and the law of Diminishing Returns: The Satellite Threshold Model

Summary The mating systems of many species comprise at least 2 alternative male mating tactics — broadly termed Dominant and Satellite tactics here. But, there exists no satisfactory conceptual framework in which to explain their co-occurrence and persistence.A Dominant male's ability to copulate is a positive, but decelerating, function of either his territory's attractiveness or his own attractiveness to females. This Diminishing Returns Effect affords mating opportunities for Satellite males associated with the most attractive sites (or males). A graphical Satellite Threshold Model, analogous to the Polygyny Threshold Model (Orians 1969), is developed to predict quantitatively the presence or absence of Satellite male tactics.Five predictions of the Model are supported quantitatively by data from dragonfly and anuran social systems and, more generally, by evidence from a wide variety of species.The Model should apply both to circumstances in which males are able to alternate between tactics and the instances in which males make an irrevocable tactical decision.     

Male capacity as related to sperm production,pregnancy initiation,and sperm competition in deer mice (Peromyscus maniculatus)

Summary Limitations on male capacity may be important to the evolution of mating strategies and behavior. Sperm counts in successive ejaculates of deer mice (Peromyscus maniculatus) decreased progressively through six ejaculations and remained depressed the following day. Males were as effective in inseminating females in cycling estrus with their second two ejaculates as with their first two and as effective in inseminating postpartum females with their fifth as with their first. In sperm competition situations males competed with rested males as effectively with their fourth, fifth, and sixth ejaculates as with their first. Thus, although sperm counts decrease in successive ejaculates, males suffer no apparent functional deficiency as long as they continue ejaculating. It is not clear whether or not deer mice are honest salesmen but they appear to be honest ejaculators and usually are honest intromitters.     

Male bird song attracts females — a field experiment

Summary The initial stage of pair formation of the pied and the collared flycatcher (Ficedula hypoleuca and F. albicollis) was simulated in a field experiment. Male dummies positioned near nest boxes and singing by means of tape-recorded song from loudspeakers offered prospecting females a nest box combined with an automatic trap. An unequivocal demonstration of female arrival at the male's territory was obtained by the trapping of the female. Control nest-box traps were provided with silent dummies. Factors other than male song causing female attraction were controlled by a daily switch of the position of singing and silent dummies. Nine out of ten females were caught in nest-box traps with singing dummies (one-tailed binomial test, P=0.011). The result supports the hypothesis that male song functions in mate attraction. This hypothesis has never previously been tested in field experiments although circumstantial evidence for it has been available.     

Correlates of male mating success in the ruff Philomachus pugnax,a lekking shorebird

Summary Male ruffs (Philomachus pugnax), a lekking shorebird, can generally be divided into two morphs according to behavior and plumage coloration. Predominantly dark-colored, independent male ruffs defend small territories on a lek, whereas lighter colored satellite males are non-territorial and less site-faithful to a particular lek. The traits associated with the mating success of independent male ruffs were studied at two leks during two seasons on the island of Öland, Sweden in May and June of 1985 and 1987. Using multivariate analyses, three characteristics were found to be significantly related to mating success: high frequency of visits by satellites to an independent male's residence, consistency of lek attendance, and low rates of aggressive behavior. In contrast, mating success was unrelated to the degree of darkness of the independent male nuptial plumage, territory location on the lek, or rate of courtship displays. The use of multivariate analyses helped to resolve conflicting conclusions from previous studies which employed simple statistical analyses, or none at all. Experimental manipulations are suggested which will help to further determine the influence of female mate choice in this lekking system.     

Sexual conflict in the house sparrow: interference between polygynously mated females versus asymmetric male investment

Summary The reproductive success of female house sparrows mated with polygynous males depended to some extent on the aid received from their mates. Polygynous males fed nestlings at the same rate as monogamous males although polygynous males gave aid almost exclusively to one of their mates (the preferred). As a consequence, the number and quality of young raised by preferred females were similar to those of monogamous females, whereas nonaided females experienced a reduction of clutch size, hatching success, and fledgling quality. Males aided the harem female that hatched her clutch earliest (in 11 out of 12 cases). However, harem females that laid eggs earliest (i.e., the potential preferred) lost eggs and/or nestlings more frequently than harem females that delayed laying. This resulted from competing females' infanticide suited for redirecting males' aid. All polygynously mated females delayed the start of a new clutch and reproduced fewer times per season than monogamous females. Consequently, monogamy seems to be the optimum mating situation for females; whereas polygynous males raised more young per year than monogamous males, interference between harem females reduced their maximum expected success.     

Temporal variation and distribution of trace metals in freshwater and fish from Calabar River, S.E. Nigeria

An investigation on the abundance and distribution of trace metals (Fe, Cu, Zn, Mn, Cr, Cd and Pb) in water, and nine species of fish samples from Calabar river was carried out in 1992. The concentrations of iron (6000–7240gl^–1), zinc (4910–7230gl^–1), and cadmium (3–7gl^–1) showed moderate pollution while those of copper (420–630gl^–1), manganese (23–48gl^–1), chromium (<10–20gl^–1) and lead (<1–10gl^–1) in water were well below WHO permissible levels. Significant seasonal changes (0.001p0.25) were obtained for iron, copper, zinc, manganese and cadmium in water. Furthermore, iron, zinc and cadmium showed statistically significant spatial changes (0.005p0.10). Of the nine fish species studied, no statistically significant relationship between body weight and the concentrations of the metals was observed. The concentrations of the metals per mean total body weight apparently decreases in the order Fe>Zn>Cu>Mn>Pb>Cd=Cr and were within the limits that were safe for consumption.     

Costs and consequences of variation in the size of ruff leks

Summary We studied 13 ruff leks in a small region on the island of Gotland (Sweden) to investigate the effect of lek size on the costs and benefits of lekking for individual males. Male ruffs occur in two behaviourally and morphologically distinct forms, independents (residents plus marginals) and satellites, whose costs and benefits we have assessed separately. These ruff leks had from 1–10 resident (territory-holding) males and were visited daily by satellites, marginals and females from 5–25 May, when most copulations occurred. We used the average number of independent males, counted during censuses taken every 5 min during 2-h observation periods at each lek, as an index of mean lek size. Per independent male, the numbers of both satellites and females increased significantly with mean lek size. Female arrival rate and attendance (total female-minutes) also increased significantly with mean lek size as did the average per capita rate of mating success for resident males (that of satellites was not quite significant). Thus, the dispersion of both of these male categories did not appear to fit an ideal free distribution with respect to mating success. In addition, the number of independent-independent fights per independent and the rate of satellite-resident dyad formation per resident increased significantly with mean lek size. These results suggest that ruffs on larger leks enjoy higher mating success than those on smaller leks but also that costs increase with lek size. We suggest that independent males distribute themselves so as to maximize their own net benefits and that this factor can account for both the occurrence of ruff leks and the variation in their size. Correspondence to: J. Höglund     

Female choice on male quantitative traits in lizards — why is it so rare?

Female choice on the basis of male traits has been described in an array of taxa but has rarely been demonstrated in reptiles. In the sand lizard (Lacerta agilis), and possibly in other non-territorial reptiles, a male's contribution to a female's fitness is restricted to his genes. In order to choose males of high genetic quality, females have to trade the fitness gain against the costs of active choice. In a Swedish population of sand lizards, long-lived males sired offspring with higher embryonic survival compared to offspring sired by short-lived males. In spite of this female sand lizards did not mate selectively with older and/or larger males. There appeared to be mo reliable cues to male longevity; age-specific male body size was highly variable. Furthermore, estimates of male nuptial coloration did not covary with ectoparasite load and, hence, females cannot use male coloration as a cue to heritable resistance to pathogenic parasite effects. When cues to male genetic quality are poor, or inaccurate, and males make no parental investment, we predict that female choice will be rare. Sand lizard females mating with many partners lay clutches with higher hatching success. Thus, females may obtain good genes for their young by multiple mating, thereby avoiding costs associated with mate choice.     

The effect of male calling on female locomotor activity of Teleogryllus commodus

Summary The calling song of the -cricket, Teleogryllus commodus, attracts for mating. Both calling and -locomotor activity are under circadian control and the behaviors occur approximately at the same time. Daily playback of calling songs for 3–12 h in constant light failed to entrain -running. Instead, calling acts as an external stimulus which can release -locomotion at any time of the 24-h period, while the clock-induced activity continues to run freely. The stimulatory effect of the calling song causes flexible extension of -locomotor activity, but a subsequent restorative period is necessary. The ecological consequences of acoustical stimulation are discussed.     

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

Summary 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.     

Circadian rhythmicity of locomotor behavior and oviposition in female Teleogryllus commodus

Summary Locomotor activity of the Teleogryllus commodus is under circadian control, with _LL=25.3 h and _DD=23.4 h. In LD 12:12 h, running occurs either exclusively during darkness (57%), mainly in the dark phase (35%), or with substantial activity peaks in both phases (8%). For oviposition, _LL>24 h and _DD<24 h; in LD 12:12 h, 80% of the studied deposited their eggs mainly during the light phase and 20% primarily during darkness. In the discussion, a temporal correlation between stridulation, spermatophore formation, and locomotion, and oviposition is established, which serves to make an encounter and mating between the sexes as likely as possible.Dedicated to Prof. Dr. M. Gersch on the occasion of his 70th birthday     

Growth and spatial distribution of Cassidulus mitis (Echinodermata: Echinoidea) on a sandy beach in Southeastern Brazil

Using a hand dredge, a population of Cassidulus mitis Krau, 1954 was sampled monthly from February 1986 to January 1987 at 15 stations offshore from Vermelha Beach (22°5718 S; 43°948 W), in water depths ranging from 0 to 6 m. The sex ratio indicated a slight numerical dominance of females for adults and a larger numerical female dominance for juveniles. A von Bertalanffy growth curve was estimated as L=71.00 (1-e^(-0.390t)), where L=length (mm) and t=time (yr). The instantaneous natural mortality rate (M) was estimated as 0.812. The population occupies a zone parallel to the beach, and displays a spatially aggregated pattern, with higher densities in areas characterized by coarse and very well sorted sand containing low amounts of organic matter.     

Temperature acclimation and other influences on embryonic duration in the copepod Pseudocalanus sp.

Embryos of Pseudocalanus sp. captured near Halifax, Nova Scotia, Canada, in spring take longer to develop than do those from the warmer waters of summer and autumn. This is related to the larger size of females and their eggs in the colder seasons. An experiment revealed size-assortative mating and the influence of male size as well on embryonic duration. The seasonal change is contrary to the slight reduction of embryonic duration after short-term cold acclimation of females in the laboratory. There is no evidence that embryos in the cold season develop more rapidly than expected from the overall relationship between embryonic duration and female size. However, they do, like embryos after short-term cold acclimation, develop relatively more rapidly at low temperatures; i.e., there is clockwise rotation of the rate-temperature response, equivalent to the temperature adaptation that has been demonstrated among species of copepods. This seasonal rotation may also be related to seasonal variations in size, since larger females from a given season produce embryos that show such rotation. Thus, there is no evidence for seasonal compensation as a consequence of temperature acclimation underlying changes that are attributable to differences in size. Evidently there is also a strong genetical component in duration of development of embryos produced by individual females.     

An advantage to mate choice in the seaweed fly,Coelopa frigida

Summary All natural populations studied of the seaweed fly, Coelopa frigida, are polymorphic for the inversion system on chromosome I. It has previously been shown that heterokaryotypes have superior egg-to-adult survival than either homokaryotype, and that there is non-random mating with respect to inversion genotypes. We have inquired whether the production of fitter progeny in larger numbers is the possible reason for the existence of non-random mating behaviour. We measured the fertility, fecundity and progeny survival of adults that have either been allowed to exercise mate preference, or been given a single, randomly chosen, mate. The fertility (% of females producing progeny) and progeny survival (% of larvae surviving to the late 3rd instar stage) are both significantly greater in choice than nochoice females. There are also significant differences in fertility and progeny survival depending on whether the parents were of similar or dissimilar inversion genotypes. An effect of relative adult size on fertility was also observed. There appear to be no effects of mate choice on fecundity. Indirect evidence is presented that adults are choosing their mates not only on the basis of genotypes but on other criteria as well. It is suggested that the superior reproductive performance of animals allowed a choice of mates may account for the evolutionary origin and continued existence of mate discrimination. Furthermore, since over 25% of the genome of Coelopa is located within inversions, the observed pattern of negative assortative mating may maintain a substantial fraction of the genes in a polymorphic state.     

Why do male Callosobruchus maculatus beetles inseminate so many sperm?

Male Callosobruchus maculatus F. (Coleoptera: Bruchidae) inseminate more sperm than females can effectively store in their spermathecae. This study examines the adaptive significance of excess sperm transfer by measuring components of male and female reproductive success in response to manipulating the number of sperm inseminated. The number of sperm transferred during copulation was reduced from 56,000 ±4,462 to 8,700±1,194 by sequentially mating males to virgin females. Reducing the number of sperm inseminated by the first male to mate had no effect on the extent of sperm precedence, but reducing the number of sperm inseminated by the second male resulted in a significant reduction in the extent of sperm precedence. When large numbers of sperm are inseminated the remating refractory period of females is increased. These results indicate that males transferring large numbers of sperm during copulation have a two-fold advantage at fertilization; they are more effective at preempting previously stored sperm and they are likely to father more offspring by delaying the time of female remating. The transfer of excess sperm does not appear to serve as nonpromiscuous male mating effort; the number of eggs laid, their fertility and the subsequent survival of zygotes were unaffected by manipulating the number of sperm inseminated. The underlying mechanisms of sperm precedence were also examined. Simple models of sperm displacement failed to accurately predict the patterns of sperm precedence observed in this species. However, the results do not provide conclusive evidence against the models but rather serve to highlight our limited understanding of the movement of sperm within the female's reproductive tract.     

Evaluation of Public Housing Lead Risk Assessment Data

A unique data set from lead risk assessments performed on 67 public housing developments from across the United States was made available for analyzes. The data set includes results of lead analysis from 5906 dust wipes and from 1222 soil samples. A total of 487 dwelling units in these developments, as well as associated common areas, were sampled, all by the same team of inspectors. The number of dwelling units within a development that were sampled reflected the guidelines then in force, the 1990 Interim HUD Guidelines, rather than those specified in the 1995 Guidelines. Median dust lead loadings for floors, 151gm^–2 (14gft^–2), and window sills, 936gm^–2 (87gft^–2), were much less than former HUD limits of 1076gm^–2 (100gft^–2) and 5380gm^–2 (500gft^–2), respectively and are only about one-third of the recently established limits of 431gm^–2 (40gft^–2) and 2690gm^–2 (250gft^–2). In contrast, the median lead loading for window troughs, 8560gm^–2 (795gft^–2), was almost identical to the HUD clearance limit of 8610gm^–2 (800gft^–2). There was a strong positive correlation between floor and window trough lead loading values for samples from the same dwelling units and those from common areas of the housing developments. Door threshold samples, which may reflect conditions exterior to the dwelling unit, were collected from 53 dwelling units. Median lead loading levels of these samples were more than ten times higher than those in floor samples from the same dwelling units, were about the same as window sill samples and about one-half of levels in window trough samples. Composite sample results, simulated by averaging results from four samples within a dwelling unit, revealed that in order to have the same rate of excedence of standards, the composite standards would have to be reduced, for example, from the single sample value of 1076gm^–2 (100gft^–2) to 527gm^–2 (49gft^–2) for floor samples and from the single sample value of 8610gm^–2 (800gft^–2) to 5160gm^–2 (479gft^–2) for window troughs. For this public housing data set, the portion of the units in developments containing more than 225 units which exceeded the established limit for window samples was the same when using either the full data set or a random one-half of the data set. This suggests that, for this data set, the number of dwelling units sampled was excessive . Thus, the required increase in the number of dwelling units to be sampled specified in the 1995 Guidelines for developments with more than 225 dwelling units, may not have been necessary if this data set is representative of public housing developments in the United States.     

Conditional lekking in ruff (Philomachus pugnax)

Summary In our study of ruff, a lekking shorebird, we found that the lek ratio — the proportion of the total population of males occurring on leks was low, averaging 12% over the breeding season (Fig. 1D). Off-lek males spent approximately the same proportion of time as lek males in displaying to females (Fig. 4). We defined three spacing tacties that male ruffs use to position themselves to court females: Following — directly pursuing females, and two types of lekking behavior, Intercepting — waiting for females at resource-rich sites, and True Lekking — waiting for females at places without any resources other than the males themselves. Males switched among these tactics, causing the lek ratio to vary over the season (Fig. 1 D). Lek ratio increased when the number of females present in the study area plummeted at the end of May, and was positively correlated throughout the season with the copulation rate of the preceding day, suggesting that males were tracking the behavior, as well as the number, of females available (Table 1, Fig. 1). Early in the season, males off leks spent most of their time feeding (Fig. 4), and lek ratio was positively correlated with temperature (Table 1), suggesting that some males may have been unable to lek during cold weather. Males on leks mated at significantly higher rates than Followers (Table 4). On average, males at our interception lek were less site faithful and less peristent than males at true leks, and the interception lek itself disappeared after females stopped coming to use its adjacent resource (Table 2, Fig. 5). The most successful individuals in our population were the True Lekking males, rather than the Interceptors.In addition to the conditinal lekking tactics described here, ruff display a dimorphism in behaviorat leks. Independent males defend small courts on leks, while Satellite males share courts and mutually display with independents Both independents and satellites may use all three conditional tactics. We propose that satellites evolved as specialized. Followers, adept at tracking the movements of females among leks.     

Sexual selection and the evolutionary effects of copying mate choice

We examine the evolutionary consequences of copying mate choice using models in which the preferences of younger females are affected by the mate choices that they observe older females making. We introduce two models of copying, termed single mate copying and mass copying, corresponding to situations in which immature females imprint on the choices of only one or of a very large number of older females, respectively. Female mating preferences are assumed to evolve only through cultural evolution, while the male trait on which they act is inherited either via a haploid autosomal or a Y-linked locus. Results show that the preference and male trait can rapidly coevolve, with a positive frequencey-dependent advantage to the more common male trait allele. This process can cause a display trait that lowers male viability to increase in a population. Mass copying results in stronger frequency dependence than does single mate copying. Mass copying and, under some conditions, single mate copying lead to two alterative stable equilibria for the male trait. Neither copying model supports variation at the male trait locus, and copying makes it more difficult for a novel male trait phenotype to spread. Correspondence to: M. Kirkpatrick     

Primary production in Dumbell Bay in the Arctic Ocean

Photosynthesis, chlorophyll, inorganic nutrients, and related factors were measured throughout a productive season in a small coastal inlet of the Arctic Ocean. Significant production was confined to 5 m for a very limited time period beacause of both light and nutrient limitations. Maximum chlorophyll was 8.2 mg Chl a m^-3 and maximum gross and net photosynthesis rates were 830 and 550 mg C m^-2 d^-1. Annual gross and net photosynthesis is estimated at about 12 and 9 g C m^-2 respectively. The effect of light stimulation on assimilation is described, sources of coastal zone nutrient enrichment are considered, and discrepancies between gross and net photosynthesis are discussed with reference to the growth characteristics of the phytoplankton population.Bigelow Laboratory for Ocean Sciences. Contribution No. 76008     

Re-copulation and post-copulatory mate guarding increase immediate female reproductive output in the dragonfly Nannophya pygmaea Rambur

After copulation, male Nannophya pygmaea dragonflies mate guard by hovering over ovipositing females and repelling conspecific males. Copulation is not always a prerequisite for oviposition in the females of this species because females can store the sperm received during previous visits/copulations. An oviposition episode consists of several bouts of oviposition separated by periods of perching. We conducted two types of male-removal experiments to examine the effects of mating and post-copulatory mate guarding on the oviposition behaviour of females. In the first experiment, we removed all males from the habitat to eliminate the effect of re-copulation, mate-guarding and harassment by males. In the second experiment, we removed males immediately after copulation to eliminate the effects of guarding and other post-copulatory male-female interactions. We compared these experimental data with data obtained under natural conditions. The dipping rate in an oviposition bout was not influenced by copulation or guarding. However, guarded females made more dips per episode than did solitary females. The proportion of time actually spent ovipositing (total bout duration/oviposition episode duration) of guarded females was higher than that of solitary females. Solitary females often oviposited in more than one territorial site, while guarded females usually oviposited within a single territorial site during an oviposition episode. Because males tend to hold territories at sites where egg survival is high, guarded females (and the male guardian) benefit from guarding in terms of egg hatchability. The possible benefits for solitary females are discussed.