Sex-Biased Parental Investment in Primates

Parental investment enhances an offspring's chances of survival concomitant with reducing the parent's ability to invest in other offspring. Three main models might explain the conditions under which parental investment is expected to be sex-biased, but accurately testing the models is difficult. At least 7 fundamental issues remain unresolved in the area of parental investment in primates. The central dilemma is trying to gauge how the process improves the survival and reproductive prospects of current progeny at the expense of the survival or fertility of the parent. No single model is likely to be applicable to all primates. Parental investment probably operates in a condition-dependent framework designed to maximize lifetime reproductive success, but whether sex-biased investment occurs in an adaptive fashion remains unresolved.     

Urbanization and Daughter-Biased Parental Investment in Fiji

Parental investment decisions guide parental actions regarding children's productive work and are shaped by ecological context. Urban ecology enhances long-term payoffs to investment in human capital, increasing opportunity costs for work performed by children, and decreased workload should result. Using an embodied capital framework, self-reported data on urban and rural Indo-Fijian children's work activities are compared. Results show higher workloads for older children, rural children, and girls. High scholastic achievement is associated with lower workloads for girls, but not boys. This pattern is interpreted as daughter-biased investment in the context of urbanization.     

Larval Feeding in Echinoderms

In all four types of feeding echinoderm larvae, particles areretained upstream from the ciliated band, probably by an inducedlocal reversal of ciliary beat. Comparative studies and theoreticalconsiderations suggest that increasing the length of the bandmay be the only means of increasing the rate at which wateris processed for paniculate food. This would account for thelong looping band and late development of adult structures inechinoderm larvae. Estimates of the minimum food requirementsof early echinplutei and of uptake of amino acids by embryosare calculated. Various means of rejecting particles are describedand observations related to nervous control of feeding and rejectionare discussed. The possible disadvantages of larvae developingfrom smaller but more numerous eggs are discussed. It is arguedthat loss of a feeding larval stage is usually an irreversibleevolutionary change in echinoderms, and some general implicationsof the irreversibility of such a change in life history arementioned.     

Growth Zones in the Echinoid Skeleton

Growth zones in echinoid skeletal ossicles are mainly the resultof differences in structural characteristics. In the test plates,opaque zones, which appear light in reflected light, dark intransmitted light, and are X-ray dense, have relatively largertrabecules and smaller intertrabecular channels. Translucentzones, which appear dark in reflected light, light in transmittedlight, and are less X-ray dense, have relatively smaller trabeculesand larger intertrabecular channels. Organic material in theplates, especially when pigmented or charred, enhances the appearanceof the growth zones. Opaque zones result from relatively fastplate growth while translucent zones result from relativelyslow plate growth; food deprivation leads to the formation oftranslucent zones. The growth zones appear to be formed seasonally,at least in some cases, probably in relation to seasonal changesin growth rates, and perhaps in relation to seasonal reproductiveactivity     

Parental Investment Strategies Determined by Expected Benefits

The purpose of this study was to determine whether parental investment decisions are made on the basis of cumulative past investment or the prospects of expected benefits minus costs. Through clutch size manipulations at nests of Redwinged Blackbirds, Agelaius phaeniceus, we obtained ♂♂ with equal past investment but varying expected benefits. Parental investment was measured by intensity of nest defense against a dummy predator at the nest. Results indicate expected benefits minus costs, rather than cumulative investment, determine parental investment decisions.     

Variability of Regeneration Mechanisms in Echinoderms

Russian Journal of Marine Biology - Several fundamentally different pathways may exist to restore a lost structure in closely related species or within the same species of multicellular animals;...     

Wnt and Frizzled Genes in Echinoderms

Russian Journal of Marine Biology - Wnt and frizzled genes of 17 echinoderm species were studied by molecular and bioinformatics methods. As a result, it has been found that echinoderms have...     

Functional Morphology of Stylophoran Echinoderms

The life orientation and mode of life of stylophorans are a subject of much ongoing debate. Examination of the ornamentation occurring both on the arm and theca in several cornutes and mitrates strongly supports the view that the life orientation was similar in all stylophorans and was ‘flat‐surface down’. The presence of an asymmetrical ornamentation adapted to hinder, or minimize, back slippage of the organism in all stylophorans gives strong support to their interpretation as mostly sessile organisms, feeding with the arm facing the current and the theca downstream. The examination of a wide array of thecal morphologies and sculpture patterns displayed by the various groups of cornutes and mitrates allows the identification of three main modes of life in stylophorans: (1) an epibenthic mode of life, with the theca as main anchor to the substrate (e.g. asymmetrical cornutes, Diamphidiocystis); (2) an epibenthic mode of life, with the arm as main anchor to the sediment (e.g. symmetrical cornutes, Peltocystis, primitive Mitrocystitida, some Kirkocystidae); (3) an infaunal mode of life, with the theca buried in a slightly inclined attitude (e.g. some Kirkocystidae, Mitrocystitida with cuesta‐shaped ribs). The partially buried mode of life of Lagynocystis is intermediate between 2 and 3.     

Why Parental Sex Ratio Manipulation is Rare in Higher Vertebrates (Invited Article)

The debate over adaptive parental sex ratio adjustment in higher vertebrates appears neither to be resolvable by the current approach, nor does it necessarily make sense. It rests on the a priori supposition of parental manipulation, which is questioned here from first principle. It is considered an unlikely biological hypothesis if we extend our perspective to gametic and offspring optimal strategies, and to the potential mechanisms existing in the avian and mammalian reproductive systems. Evenness of primary sex ratios is expected to be optimal from the gametic point of view and is supposed here to be the more likely evolutionary outcome. Also, manipulations by sex-selective offspring mortality is argued to be unlikely as usually the benefits will be surpassed by the costs incurred. Furthermore, parents can adjust behavioural and energetic investment patterns to their offspring sex (ratio), thereby minimizing any costs of sex ratio control inability. Slight biases in offspring sex ratios are then viewed as resulting from physiological limitations ultimately relating to sex differences in embryonic development. Contrary to recent attempts to understand higher vertebrate sex ratio variation by further refinement of functional models (of parental optima) and data analysis, Bayesian logic precludes those approaches to gain useful new insights. To prove the basic assumption of parental manipulation, apart from defining gametic and offspring optima, the emphasis should lie on identifying control mechanisms by experimental verification.     

The Primary Parental Investment in Children in the Contemporary USA is Education

This paper tests the Trivers-Willard hypothesis that high-status individuals will invest more in sons and low-status individuals will invest more in daughters using data from the 2000 to 2010 General Social Survey and the 1979 National Longitudinal Survey of Youth. We argue that the primary investment U.S. parents make in their children is in their children’s education, and this investment is facilitated by a diverse market of educational choices at every educational level. We examine two measures of this investment: children’s years of education and the highest degree attained. Results show that sons of high-status fathers receive more years of education and higher degrees than daughters, whereas daughters of low-status fathers receive more years of education and higher degrees than sons. Further analyses of possible mechanisms for these findings yield null results. We also find that males are more likely to have high-status fathers than females.     

Mating Costs versus Parental Investment: A Reply to Gwynne

Dewsbury, D. A., ed. (1985): Foundations of comparative psychology (Zur Geschichte der vergleichenden Psychologie). Benchmark Papers in Behavior Series. Toates, F. (1986): Motivational systems (Antriebe). Le Magnen, J. (1986): Hunger. Rosenblatt, J. S., C. Beer, M.-C. Busnel, & P. J. B. Slater, eds. (1985): Advances in the study of behavior. Dickerson, J. W. T., & H. McGurk, eds. (1982): Brain and behavioural development. Interdisciplinary perspectives on structure and function (Gehirn und Verhaltensentwicklung). Bisping, R. (1985): Gedächtnisübertragung bei Goldfischen. Experimentelle Untersuchungen in der “shuttle-box” mit besonderer Berücksichtigung des Problems der Reizspezifität unter einer Rot-Grün-Diskriminationsbedingung (Memory transfer in goldfish). Nachtigall, W. (1984): Erfinderin Natur: Konstruktionen der belebten Welt (Natural constructions). Rasch und Röhring Verlag, Hamburg und Zürich.     

Behavioral Development and Parental Investment in Captive Bongos (Tragelaphus eurycerus)

SYNOPSIS. The bongo is one of the least-studied of the Tragelaphini.In a study of five captive bongo calves, two males and threefemales, we measured several behaviors important to parentalinvestment theory (Clutton-Brock et al., 1982), in order todescribe their pattern in a rare species, and add to the databasepertaining to sex allocation theory. Variations in individualpatterns of maternal investment, such as suckling rate and boutlength, were measured and graphed over time, with sex of calf,and age and dominance of dam indicated. Instances of "thiefsuckling" by calves and juveniles were also described in termsof kinship among the animals involved. Only one measure of maternalinvestment was biased in favor of males, which had a somewhathigher birth weight than females. Other measures showed littlesex difference. Among these calves, maternal care appeared tovary more with dominance and age of the dam than with sex ofcalf. Data from these animals generally conform more closelyto those of Byers and Moodie (1990). They found little evidenceof sex-biased investment among pronghorn (Antilocapra americana)fawns, and postulated that many ungulates have such a high rateof development that further differential investment is impossible.Robust biological theories are supported by data obtained froma wide variety of species, many of which are impossible to studyclosely in the wild. Additional studies on captive populationsof sexually dimorphic species would contribute usefully to theaccumulation of data pertinent to parental investment theory.     

Observations on the Activity of Echinoid Pedicellariae

The tridentate, ophiocephalous and globiferous pedicellariae of sea‐urchins react to specific stimuli of the test so that they become alert. Their jaws open, exposing their special receptors, and their stems move them towards or away from the stimulus. Stem movements are coordinated so that the jaw reflexes may alleviate the stimulus. When the stimulus ceases the animal usually settles down so that most of the pedicellarial jaws close and the stems lower. This quiescence reduces the chances of self attack, and may allow commensals to move freely. These stem movements parallel those of spines in covergence and divergence responses even on isolated test fragments, and it would appear that they are coordinated by the basi‐epithelial nerve plexus of the test. Experimental lesions and photography have been used to analyse this coordination and a theoretical form for it is proposed.     

Low Socioeconomic Status and Female-Biased Parental Investment: The Mukogodo Example

Hierarchies of wealth and ethnic prestige among East African herders present an opportunity to test the Trivers-Willard hypothesis that low socioeconomic status should correlate with female biases in parental investment. The Mukogodo are at the bottom of such a regional hierarchy due to their poverty and low status as former hunters. As a result of these factors, Mukogodo men have lower polygyny rates than their neighbors, and Mukogodo women have higher mean reproductive success than Mukogodo men. The data fulfill the prediction that there should be a bias in parental investment in favor of daughters. The sex ratio of the 0–4 age group and the reported sex ratio at birth are both female-biased. Although there is no evidence of infanticide, sons may be neglected in favor of daughters. Evidence from a dispensary and from a clinic run by a Catholic mission both show that the Mukogodo take daughters for treatment more often than they take sons. Also, daughters may be nursed longer than sons.     

Parental Investment and Division of Labor in the Midas Cichlid (Cichlasoma citrinellum)

The Midas cichlid (Cichlasoma citrinellum) is an aggressive, monogamous fish living in the Great Lakes of Nicaragua. Its breeding success rates are low due to intense competition for breeding sites and high levels of predation on the young. Male Midas cichlids devote a small portion of body weight to gonads and gametes compared with females. Males produce relatively small amounts of sperm perhaps because cichlid fertilization is very efficient and the male has a high certainty of paternity. While pair members invest equal amounts of time in parental care over the course of the breeding cycle, there is a clear division of labor. Males invest more in territorial protection than do females, whereas females provide more nurturance. Both parents are active over the course of the cycle but the male invests more intensely in the early stages of the cycle. About the time the eggs hatch, the burden of care shifts to the female and she continues to invest significantly more than the male over the remainder of the cycle. Females invest much more than do males when tissue investment and parental behavior are combined. Females also assume more of the burden of care as the brood matures. The male is not free to take advantage of this and leave his mate to initiate other broods because two parents are needed to defend the breeding site and brood. Monogamy with biparental care results.     

Echinoderms (Echinodermata) of the Mexican Caribbean

A systematic list of the echinoderms of the Mexican Caribbean based on museum specimens of the Colección Nacional de Equinodermos, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México and the National Museum of Natural History, Smithsonian Institution, Washington, D.C. is presented. This list reveals an important echinoderm biodiversity in the Mexican Caribbean, where five of the six echinoderm classes are represented. A total of 178 echinoderm species is recorded, distributed in 113 genera, 51 families and 22 orders. 30 new records for the Mexican Caribbean are presents: Crínoidea (three), Asteroidea (two), Ophiuroidea (eleven), Echinoidea (one), Holothuroidea (thirteen).