Diversity Of Reproductive Strategies Research Articles

Parental investment and the evolution of subsocial behaviour in harvestmen (Arachnida Opiliones)

The diversity of reproductive strategies within the arachnids rivals all other arthropod groups. However, with the possible exception of spiders and scorpions, evolutionary biologists have overlooked these organisms. The order Opiliones is divided in three suborders (Cyphophthalmi, Palpatores and Laniatores) with considerable differences in morphology, habits and behaviour. In this review we focus on the life history, sexual behaviour and ecology of Opiliones, and discuss the possible causes of the diversity of forms of parental investment found in this order. In the Cyphophthalmi the forms of parental investment are restricted to the choice of oviposition sites. Among the Palpatores there is selection of microhabitats for oviposition, egg-hiding, and discharge of repugnant secretions on the eggs. The most common form of parental investment in Laniatores is probably egg-hiding by females but several species show subsocial behaviour, including both maternal and paternal care. The scarcity of paternal care among harvestmen and the differences when it does occur suggest that male care evolved independently in different laniatorean lineages from a plesiomorphic state of non-care rather than from female care. Both male and female care reduce egg mortality. Egg predation, rather than infection by fungi may be the most effective pressure favouring the evolution of subsocial behaviour in harvestmen. Subsocial behaviour appears to be restricted to members of the Laniatores since they show a conjunct of preadaptations that may favour prolonged associations between the parental and the offspring such as, restriction of the reproduction effort to specific periods and places, considerable adult longevity, and aggressive mechanisms of defence. On the other hand, many of these preadaptations mentioned are absent in the Palpatores. Reduced fecundity and increased egg size accompanied the evolution of subsocial behaviour in laniatorean harvestmen. Palpatores, which show very simple forms of parental investment, have significantly higher fecundity and a smaller egg size than Laniatores, which show subsocial behaviour.

Spatial and Temporal Distribution of Vocalising Maile Bearded Seals - Implications for Male Mating Strategies

The bearded seal, Erignathus barbatus , is an ice breeding phocid that mates in the water. The most detailed studies of male behaviour among aquatic-mating phocids have concentrated primarily on temperate breeding harbour seals, Phoca vitulina , where females are dependent on stable substrates, rock or sand, for parturition. In contrast, female bearded seals give birth on ice floes or the edge of fast ice, a highly unstable substrate. In this study, spatial and temporal patterns of male bearded seal vocalisations were studied in Kongsfjorden, Svalbard from April 1999 to the end of May 2000. Males vocalised during a discrete 90-day period from early April to mid July, no calls were heard at any other time of the year during this study. Vocalisations increased in duration towards the middle of the mating season in late May, although no change was seen in inter vocal intervals of individuals. The frequency of occurrence of vocalisations varied significantly with the diel cycle. Vocalisations increased in number from 16:00 hrs onward into the 'night', peaking around 04:00 hrs. This peak coincides with the period when most females are in the water. Female bearded seals were found throughout Kongsfjorden. Their distribution at any particular point in time depends on the availability of suitable haul-out sites ( i.e. ice conditions), which are highly variable over time spans as short as a few hours. Males vocalised in higher densities around the fjord entrances and may use these 'geographical bottlenecks' to intercept passing females. We suggest that male distribution may reflect the unpredictable nature of female distribution. Aquatic mating phocids appear to exhibit variations in reproductive strategies, including spatial arrangements of displaying males, which reflect the varying constraints imposed on female movement patterns by their local habitats and ecological requirements.

Geographic variation in the sex ratio, sex specific size, and age structure of Plectropomus leopardus (Serranidae) between reefs open and closed to fishing on the Great Barrier Reef

Variation in reproductive parameters of Plectropomus leopardus populations between coral reefs open and closed to fishing was examined in two geographic regions (off Townsville (19°S) and in the Swains (22°S)) of the Great Barrier Reef, Australia. The reproductive parameters that were examined included the operational (reproductive) sex ratio and size and age structure of mature females, sex-changing individuals (transitionals), and mature males. There was a greater proportion of males above the minimum size and age of harvest on reefs closed to fishing for 8-10 years than on reefs open to fishing, although the effect varied with geographic region. Nevertheless, neither the sex ratio, mean age, nor mean size of males or transitionals varied significantly with reef closure status. Females, however, were significantly older and larger on closed than on open reefs in both regions. Marked regional variations in the sex ratio and average age of transitionals were found independent of reef closure status, suggesting regional variation in reproductive strategies. Controlled manipulations, inclusion of broad spatial scales, and detailed studies of intra- and inter-specific variation in serranid reproductive biology are necessary to resolve such complexities in the responses of protogynous serranids to fishing pressure and management strategies.

Population Genetics of the SilversideOdontesthes argentinensis(Teleostei, Atherinopsidae): Evidence for Speciation in an Estuary of Southern Brazil

Allozyme electrophoresis was used to investigate genetic population structure among 245 individuals of the silverside Odontesthes argentinensis sampled from localities in southern Brazil and Uruguay. Striking differences in allozyme frequencies and genetic variability were detected among localities. Analysis of these differences indicated two distinct populations: one distributed in a wide marine coastal zone; and one in the peripheral environment of the Patos Lagoon estuary in southern Brazil. The population in Patos Lagoon appears to have originated from an ancestral marine population and been established in the estuary by a founder effect. The extent and pattern of genetic divergence found in our study, the existence of diverse reproductive strategies in the estuarine silversides, and differences in morphology of eggs and larvae, indicate that speciation is taking place in Patos Lagoon. It is suggested that the two populations should be considered separately when formulating management and conservation strategies.

Variation in sexual and clonal reproduction among introduced populations of flowering rush, Butomus umbellatus (Butomaceae)

Butomus umbellatus L. is an invasive emergent aquatic plant that exhibits wide variation in seed production. Native European populations are fertile and diploid or sterile and triploid. However, adventive North American populations are widely reported to be sexually sterile. We quantified sexual fertility and self-compatibility under greenhouse conditions for nine introduced populations from eastern Ontario, Canada. All populations were highly fertile and self-compatible. Each flower produced an average of 127 ± 7 (mean ± SE) filled seeds and 31.4 ± 0.4% of seeds germinated. This level of fertility is much higher than previously reported, even for fertile native populations. We also quantified the production of seeds, flowers, and inflorescence-borne asexual bulbils in 19 natural populations from eastern Ontario; 17 populations were highly fertile (200 ± 9 seeds/fruit) and 2 produced almost no seeds (0.0-0.3 seeds/fruit), because ovules were either not fertilized or were aborted soon after fertilization. We found no evidence of a trade-off between sexual reproduction and clonal reproduction via bulbils. The wide variation in reproductive strategy observed in these populations raises questions concerning the evolutionary loss of sex in clonal populations, and may have significant implications for the spread and management of this exotic species.Key words: aquatic plants, clonal reproduction, breeding systems, invasive plants, reproductive ecology, sexual sterility.

Main Neuro-Endocrine, Endocrine and Paracrine Regulations of Fish Reproduction, and Vulnerability to Xenobiotics

The reproductive function of fish, which is very sensitive to the variations of environmental factors, appears also to be particularly vulnerable to the presence of xenobiotics in the aquatic medium. Many physiological processes can be impaired, from sexual differentiation to female and male gametogenesis, due to disruptions among complex neuro-endrocrine, endocrine or paracrine regulations. This paper describes the main regulation steps that are known or can be suspected to be disrupted by xenobiotics and gives some examples. The large interspecific diversity of reproductive strategies and the complexity of underlying mechanisms are particularly highlighted to draw attention to possible confusions between real endocrine disruptions and natural physiological variations.

Reproductive strategies and energetic adaptations of polar zooplankton

Summary Key factors governing polar ocean ecosystems are low temperatures and a pronounced seasonal variability of ice cover, light regime and primary production. Depending on their ecological niche and trophic position, zooplankton species at high latitudes have developed a variety of reproductive strategies and energetic adaptations to cope with these extreme environmental conditions. Life-cycle strategies of the herbivorous copepods and euphausiids, which make up the major portion of polar zooplankton biomass, include seasonal vertical migration, dormancy (diapause, quiescence) and the accumulation of energy reserves. These lipid stores help to buffer the pulsed seasonal food supply, and they play an important role in fueling reproduction independent of phytoplankton. Only a smaller fraction of the lipid reserves accumulated during spring and summer are usually catabolized for metabolic maintenance during the food-limited dark season. These deposits are retained until the end of winter and allow early egg production and spawning prior to—or coinciding with—the onset of vernal primary production. It enables the new generation to make full use of the short productive season for growth and development to reach viable overwintering stages. The Antarctic krill Euphausia superba is an exception since it uses its depot lipids for metabolic maintenance during the dark season. It therefore relies on external resources (Primary production) for reproductive processes, resulting in a later spawning period as compared to the other euphausiids. Another important component of the herbivorous Antarctic zooplankton, the salps, have developed a very different reproductive strategy. They are able to switch from sexual reproduction to asexual budding (metagenesis), which allows extreme multiplication rates under favourable feeding conditions. Due to these successful adaptations, herbivores are able to build up huge stocks, in spite of the short productive period. Omnivorous and carnivorous zooplankton species, e.g., amphipods or chaetognaths, are not much constrained by the seasonality problem, but experience a more constant food supply. They show a tendency towards K strategies with a prolonged reproductive period, reduced egg numbers and increasing parental care. However, they do not exhibit such typical “polar adaptations” as developed by the herbivorous species.

Annual broadleaf crop frequency and residual weed populations in Saskatchewan Parkland

The development of problematic weed populations is a concern in western Canadian fields where canola and pea are grown in a 4-yr sequence with spring cereal grains. Weed densities were examined at a site near Melfort, Saskatchewan, Canada, from 1994 to 1997 in seven zero-till managed crop rotations. Four rotations that included canola, pea, or flax in at least 3 of 4 yr (HBF: high broadleaf–crop frequency) were compared with three rotations that included broadleaf crops grown in 2 of 4 yr (LBF: low broadleaf–crop frequency). Spring wheat and barley were the cereal crops in rotation. Residual (postherbicide application) weed density for each weed species in a given year was summed across all phases for each rotation to reflect the overall weed infestation. Four annual broadleaf weed species were most abundant in 1996 and a second group of three species, having a variety of reproductive strategies, became progressively less abundant as the study progressed. The difference between the HBF and LBF rotations for the density of these species varied and was most prominent in years when environmental conditions were conducive for their growth. More frequent applications of ethafluralin, with its residual weed control, best explained why wild oat and catchweed bedstraw generally were less abundant in the HBF rotations. Of particular interest was the 8 plants m−-2greater density of dandelion and perennial sowthistle in the HBF vs. LBF rotations in the last year of the study. It is thought that the limited herbicide options for the control of these species could present a future problem if they continued to develop in the HBF rotations. Differences in herbicide use between the HBF and LBF rotations were considered the primary factor controlling the rotation effects on weed density.

The meanings of weaning: Growth, lactation, and life history

Hooded seal pups are suckled for a total of four days; chimpanzees and elephants sometimes are suckled for as long as eight years. This enormous range suggests considerable diversity in reproductive strategies. Lactation represents early maternal effort, whereas weaning is the infant's transition to nutritional independence. Weaning behavior is thus important from two interconnected perspectives: that of the infant during this transition and that of the mother with the cessation of lactation and the resumption of her reproductive capacity. What controls such diversity in the duration of lactation? What are the consequences of this diversity for mothers in terms of reproduction and for infants in terms of their growth and survival? How are differences in lactation reflected in behavioral interactions? The answers to these questions involve consideration of weaning and growth, and have implications for life histories.

Continuous variation in reproductive strategy as an adaptive response to population density in the moth Plodia interpunctella

Despite being variable, reproductive environments may be predictable. Because of this variability, individuals may maximize fitness through phenotypic plasticity. Here, I describe how males of the moth Plodia interpunctella are sensitive to population density during larval development (controlling for confounding effects of diet), and tailor a strategy which best suits the predicted reproductive environment. Such a strategy may be adaptive for this semelparous species, where all resources for reproduction are accrued during larval development and adults have a brief reproductive stage. Population density influences female mating pattern: at high densities, females mate more frequently, thus generating greater risks of sperm competition. Males reared at higher densities take longer to develop, despite achieving the same body mass. Adults from high densities have relatively larger abdomens and testes, produce greater numbers of sperm and live for shorter periods. At lower densities development time is reduced, and adult males have relatively larger heads and thoraxes, relatively smaller testes, ejaculate fewer sperm and live for longer periods. These results suggest that developing male P. interpunctella detect signals which reflect larval population structure, and hence eventual mating pattern. Males at low densities anticipate rare mate encounter and low risks of sperm competition, and therefore appear to invest in competence for migration and mate-searching. Males at higher densities anticipate frequent mate encounter and high risks of sperm competition, and therefore appear to invest in competence for mating and sperm competition. Such flexible male responses represent a ‘reaction norm’ where male strategies vary as a continuous function of the predicted reproductive environment’s signal.

Reproductive Strategies in Relation to Prey Size in Altricial Birds: Homage to Charles Elton

An examination of the prey size of 101 altricial bird species showed large interspecific differences in the gross energetic content of the prey items. These differences in prey size were related to variation in reproductive strategies of this group. In accordance with the argument presented by the English ecologist C. Elton, a lesser amount of food was brought to the nest in taxa of altricial birds specializing on small prey items. However, this relation disappeared after controlling for the effects of body weight. Two changes are likely to evolve as a response to a reduced ability by the parents to provision their offspring. A decrease can occur either in the clutch size or in the growth rate of the nestlings. The comparative analyses showed, after controlling for the effects of body weight and phylogeny, that in altricial birds a smaller clutch size was found in those species specializing on small prey items, whereas growth varied independently of prey weight.

Ecological Consequences of Sexual versus Asexual Reproduction in Dicranum flagellare and Tetraphis pellucida

To test hypotheses of the relative advantages of sexual and asexual reproduction, the reproductive ecology ofDicranum flagellare is compared to that ofTetraphis pellucida. Both species share a habitat preference for decaying logs of the forest floor, but they differ in reproductive mode. In D. flagellare asexual reproduction predominates, whereas T. pellucida produces both sexual and asexual propagules. The ecological consequences of reliance on asexual reproduction are explored: dispersal, colonization, and spatial distribution. The asexual brood branches of D. flagellare suc- cessfully colonize gaps produced by disturbance, but only when D. flagellare is present in the nearby vegetation. The local distribution ofD. flagellare is limited to spatially aggregated substrates, whereas T. pellucida is widely dispersed. Dicranum flagellare invests significantly more biomass in asexual reproduction, but the overall reproductive effort of T. pellucida exceeds that of D. flagellare. Brood branches of D. flagellare germinate significantly more rapidly than Tetraphis gemmae. Dicranum flagellare persists longer than T. pellucida in log communities, perhaps as a result of accumulation of perennial shoot increments. The distribution of bryophytes through a wide range of transient microhabitats reflects the evolu- tion of diverse reproductive strategies. Bryophyte life histories range from fugitive species that rely on sexually produced spores to species whose repro- ductive effort is entirely asexual. The adaptive sig- nificance (if any) of these reproductive patterns is not well understood (Mishler 1988). It has been suggested that bryophyte reproduction involves a balance between the long-term advantages of sexual reproduction and the more immediate benefits of asexual propagation (Cummins & Wyatt 198 1). The nature of this balance may shift with changing en- vironmental conditions--in particular, the distur- bance regime. Recent studies demonstrate that ad- aptation to disturbance frequency may be a strong selective pressure on the reproductive ecology of the forest floor bryophyte Tetraphis pellucida (Kim- merer 1991a,b, 1993).

Individual Differences among Female Rats in the Timing of the Preovulatory LH Surge Are Predicted by Lordosis Reflex Intensity

In young female rats, we found individual differences in LH surge characteristics that could underlie differences in fertility throughout adulthood and aging. We modified a jugular cannulation technique, which enabled us to characterize four successive proestrous LH surges in regularly cycling female rats. During a surge, the timing and amount of LH were negatively correlated, so that late-onset surges reached a low peak, late in the day. Within a female rat, the timing of the LH surge, but not the blood level of LH, was stable from cycle to cycle. Thus, differences in onset and peak time between successive LH surges within one female were less than differences among females. Moreover, these individual differences in timing of the LH surge were positively correlated with individual differences in lordosis reflex intensity on proestrus. Females with early-onset LH surges had high average lordosis reflex intensity on proestrus. Therefore, lordosis reflex intensity is a nonintrusive behavioral biomarker for individual differences in the timing of the preovulatory LH surge. This relationship between behavior and the preovulatory LH surge may reflect a hormonal basis for variations in reproductive strategies throughout the life span.

Variation in Reproductive Strategy Among Clones of the Bryozoan Celleporella Hyalina

To test alternative hypotheses concerning life history flexibility in variable environments I focused on the genotypic and environmental components of variation in Sex Ratio and Reproductive Allocation in clones of a benthic modular animal, the bryozoan Celleporella hyalina, grown in different flow regimes through all seasons. Clones of this bryozoan growing in autumn and winter varied significantly in growth rate, modular sex ratio, and relative investment in sexual reproduction. Experimental reduction of ambient water flow significantly reduced growth rate but did not affect Reproductive Allocation or Sex Ratio. Clonal differences in Reproductive Allocation were associated with a trade—off between somatic and sexual functions: clones investing more heavily in sex reached a smaller somatic size. In spring and summer, Celleporella clones showed an inconsistent and less pronounced growth response to flow regime. Significant genetically based variation was found for all measured characters except Reproductive Allocation. In both seasonal groups, clonal Sex Ratio was genetically canalized, and insensitive to the experimental treatments. The presence of clonal variability in Reproductive Allocation in autumn/winter but not in spring/summer may arise from seasonal differences in lifespan on natural substrata. These may select for maximal sexual investment in short—lived generations, but allow scope for alternative strategies if potential longevity is greater. The genetic constraint on clonal Sex Ratio may not conflict with models predicting flexible sex expression in variable environments, since the seasonal fluctuations experienced probably do not affect sex—specific reproductive success. The small Genotype × Treatment interactions and the positive correlations between clonal performance in differing treatments and seasons, suggest that the relative fitness of clones does not vary, a result at odds with assumptions underlying current hypotheses for the adaptive basis of sexual reproduction.

Differential allocation of reproductive effort to territorial establishment and maintenance by male yellow warblers (Dendroica petechia)

We tested the hypothesis that the basis of the variation in reproductive strategy among male yellow warblers (Dendroica petechia) is a tradeoff in the allocation of reproductive effort to intrasexual competition (territorial effort) and to parental care (parental effort). Since a negative correlation between level of parental effort and amount of brown streaking on the breast (plumage score) has already been demonstrated in this species, this study looked for evidence of a positive correlation of territorial effort with plumage score and a negative correlation with parental effort. Analysis of the spatial and temporal use of territories, prior to egg-laying, by males with different plumage scores supported the prediction that brighter (higher plumage score) males allocate more effort to territorial establishment and maintenance (Fig. 1). Male plumage score was positively and highly significantly correlated with six different measures of the relative amount of time spent, rate of energy expended, and risk of injury assumed by each male during territorial activities. The level of territorial effort was also found to be negatively correlated with the level of parental effort expended by the same males later in the season, confirming that there is a tradeoff in allocation of reproductive effort to these two major components. Further analysis revealed that territory quality was positively correlated with male plumage score (Figs. 3 and 4), while average nestling growth rate and other indices of reproductive success were not (Fig. 6). These results suggest that increased territorial effort by brighter males enables them to occupy higher quality territories where high levels of parental effort are not necessary to maintain high levels of reproductive success. Since reproductive success was not correlated with plumage score, this study further supports the differential allocation hypothesis that different males are using alternative strategies for the allocation of reproductive effort.

Spatial heterogeneity and niche differentiation in oceanic zooplankton

The annual mean abundance (1958 to 1986) and geographical distributions of four of the major biomass species of copepod in the northern North Atlantic Ocean are shown together with their seasonal vertical distributions (1971 to 1974) from Ocean Weather Station I. The arcticboreal species Euchaeta norvegica and Calanus finmarchicus have sympatric distributions with their maximum numerical abundance in the cold water current system between Labrador and Greenland. The distribution of the temperate species Pleuromamma robusta and Metridia lucens are allopatric with respect to the two previous species but have sympatric distributions centering around the north-eastern oceanic region. The four species dominate the copepod biomass of the oceanic epiplankton and minimise interspecific competition by a) seasonal displacement of their main reproductive periods, b) occupying different trophic levels, c) having diverse reproductive strategies, d) residing in different positions in the water column and e) having different migratory behaviour throughout the year. The vertical distributions and migratory behaviour of these four copepods suggest a highly structured community with individual species occupying distinct niches with minimum overlap between competitors; even though the vertical distributions of the species are constantly changing through diel, ontogenetic and seasonal migrations.

Sexual selection and variation in reproductive strategy in male yellow warblers (Dendroica petechia)

Male yellow warblers (Dendroica petechia) exhibit extensive variation in the amount and conspicuousness of the sexually distinctive brown streaking on the breast. We investigated this intraspecific variation in degree of sexual dichromatism to see if male plumage rank (essentially the amount of brown streaking) is correlated with the amount of reproductive effort allocated to parental investment, as sexual selection theory would predict. As predicted, the average rate of feeding visits to the nest by males was negatively correlated with the plumage rank of the male in 1982 (Fig. 1) and 1983 (Fig. 2), and varied little between years or among study areas. Within one study area, the higher nest visit rate of dull (low plumage rank) males was correlated with higher nestling growth rates. But in the other two study areas, where bright (high plumage rank) males predominated, nestlings of bright males tended to have the highest growth rates despite minimal nest visit rates. Thus, overall there was no correlation between male plumage rank and nestling growth rate, a potential index of relative reproductive success, in either year (Figs. 3 and 4). This overall equal nest success likely helps to maintain the behavioral and plumage polymorphism. Since we could find no evidence that the high nestling growth rates of bright males were due to an adjustment of female parental effort to compensate for low male parental effort, there must be some other benefit of being bright which contributes to nest success. To address this, we used the relationship between parental feeding rates and nestling growth rates for each nest as an index of relative territory quality. This analysis suggests that bright males generally occupy the best territories available, possibly because they are more aggressive in obtaining and defending them than dull males. Dull males appear to be relegated to poorer territories, where an increase in male parental contribution would be necessary to achieve high nestling growth rates. We propose that different males are using alternative but evolutionarily stable reproductive strategies, in a way that is consistent with the predictions of sexual selection theory. Allocation of limited reproductive effort to parental investment decreases as sexual dichromatism increases, which probably reflects an increased investment in intermale competition for the best territories.

Sexual Reproduction of Two Intertidal Sea Anemones (Coelenterata: Actiniaria) in Malaysia

Sexual reproduction in actinians Anthopleura handi Dunn and Haliplanella luciae (Verrill) was studied through one year at Jeram, on Malacca Straits. No evidence could be marshalled to support periodicity in gametogenesis of either species. The absence of cyclicity in prevalence and size of internally brooded young of A. handi substantiates this finding for species. Female, sterile, and hermaphroditic anemones brood. The sex ratio of smaller individuals is heavily biased toward females; that of larger anemones is more balanced, suggesting that some but not individuals are protogynous. Sterile and hermaphroditic brooders are inferred to be transitional from female (when young are produced) to male (by which time young have been released). Only sterile and female individuals of H. luciae were found. Although as many as half anemones may bear eggs at any time, absence of males presumably precludes sexual reproduction. Asexual reproduction by pedal laceration appears to be sole means of progagation. THEORIES ABOUT ANNUAL REPRODUCTIVE PERIODICITY were developed from data on temperate species. Environmental cues triggering phases of cycles, or entraining endogenous rhythms, are those that vary conspicuously and include photoperiod and temperature (Welty 1962, Giese and Pearse 1974). Semper (1881: 135, 136) was apparently first to propose that in tropics, where such factors may vary little and unpredictably, all periodicity, as regards summer and winter, must be entirely lost, and at last fully grown individuals and young ones, larvae and freshly laid eggs will be found together at every season and in every month of year. In Philippines he noted the total absence of periodicity in life of sea animals, particularly Invertebrata; among these I could not detect a single species of which I could not at seasons find fully grown specimens, young ones, and freshly deposited eggs, although he went on to remark that lack of periodicity is not unknown in cold seas. Most early studies on reproductive periodicity of tropical marine invertebrates consisted of single samples of a species in various parts of its range (e.g., Pearse 1968), or sustained sampling in areas at margins of tropics (e.g., Pearse 1978). Recently, as data from prolonged research in equatorial tropics have accumulated, it has become clear that tropical species, like temperate ones, engage in a variety of reproductive strategies, including annual cycling tied to environmental cues, local cycling that differs among populations, short-term cycling tied to factors such as tides and moon, and lack of cycling altogether (e.g., Berry 1968, Vohra 1970, Lessios 1981). This is first long-term investigation to document sexual reproduction in an equatorial actinian. The major subject of study, actiniid Anthopleura handi Dunn 1978, was of especial interest because it broods its young internally (Dunn 1978). Examined for comparison was sympatric acontiate Haliplane/la luciae (Verrill 1898), which is of interest because it is probably most widely distributed

Food Habits, Energetics, and the Population Biology of Mammals

Data presented in this paper suggest that a complex interaction occurs between the physiological parameters of mammals and the growth and fluctuation of their populations: The Malthusian parameter rm increases with rate of metabolism, which in turn varies with body size and food habits. It can be concluded that it behooves all mammals to have as high a rate of metabolism as can be sustained by the quantity and quality of their food resources in space and time, because this adjustment will permit them to maximize their reproductive efforts. These interactions raise many questions, one of which concerns the temporal variation in reproductive strategies. Thus, Coady (1975) showed that the basal rate in the brown lemming (Lemmus trimucronatus) may be especially high during a winter in which the snow cover is reduced. Does a seasonal variation in the rate of metabolism therefore have a significant influence on seasonal variation in reproduction and therefore in population size? Whatever the correct answer to t...

Stable equilibrium strategies and penalty functions in a game of attrition

Maynard-Smith (1974) has presented a game of attrition model for animal conflict. He assumed that the penalty function, giving the cost in terms of fitness, of displaying for a given time period, is a linear function of the time of display. Under this assumption he shows that an evolutionary stable strategy (ESS) always exists: one such is a mixed strategy for which display times have a negative exponential distribution. Given the diversity of reproductive strategies and patterns of agonistic behavior in nature, it is reasonable to consider games with different types of cost functions. In this paper it is shown that if more general cost functions are allowed (not necessarily linear), then ESS's still exist and give a great variety of distributions of display time. Supporting data are presented to suggest that these distributions may be found in nature. It is suggested that the interrelations between an animal's fitness budget and the game's penalty function will determine the nature of an ESS for different kinds of games.