A statistical model of the reproduction of aphids

1. The logistic function has been generally used to describe the reproductive process of a “population” of animal. However, this model can not give us any information about the reproductive process of “individuals” in the population. In this study a statistical model on the basis of the reproduction of individuals of barley aphid is presented to find the proportion of the mature individuals, the heterogeneity in reproductive ability of the aphids, etc.
2. The model is constructed as follows:
3. The probability that j insects are found on a plant at time t₀ is represented as Q(j).
4. The probability that h individuals of j have reproductive ability, say, mature individuals, in the period t₀ to t₁ is represented as B(h/j)=_jC_hw^h(1−w)^j−h, where w is the proportion of mature individuals.
5. In a population with a homogeneous reproductive ability, the probability that each parent lays i offspring in the period t₀ to t₁ is represented as P(i/m)=e^−mmⁱ/i!, where m is mean. And, in a population, m changes according to the gamma distribution. Hence the probability that a parent lays i offspring between t₀ and t₁ is represented as , where p and k are parameters of negative binomial distribution. The probability that h parents on a plant lays s offspring is represented as .
6. From the assumptions mentioned above, the probability that s offspring are to be found at time t₁ on a plant with the original j individuals at time t₀ is represented by
7. The experimental populations were demonstrated to fit well to the model.

     

Lifetime reproductive success in reproductively suppressed female voles

A population of the grey red-backed vole, Clethrionomys rufocanus bedfordiae, was investigated on a 1 ha control grid and a 1 ha grid on which the voles were fed within a 2.1 ha outdoor enclosure in Hokkaido, Japan by live trapping from 1984 to 1986, for testing the Reproductive Suppression Model of Wasser and Barash (1983)-females can optimize their lifetime reproductive success by suppressing reproduction when future conditions for the survival of offspring are likely to be sufficiently better than present ones as to exceed the costs of the suppression itself. Age at the first pregnancy more varied in a higher density population on the experimental grid and females could be classified into the early and the late reproductive type in two generations (A: females born from February to June 1985; B: females born from September to November 1985). Lifetime reproductive success (the number of pregnancies, the number of successful litters, and the number of offspring) was not different between the early and the late reproducing females. The late reproducing females lived for longer periods than the early reproducing females, so that the loss by delayed start of reproduction was compensated for by a longer life span. Life span was not different between offspring of the early and the late reproducing females. These facts supported the Reproductive Suppression Model.     

The reproductive biology of the cyprinid, Thynnichthys thynnoides (Bleeker), in the Chenderoh Reservoir — a small tropical reservoir in Malaysia

The reproductive biology and breeding cycle of a tropical cyprinid, Thynnichthys thynnoides (Bleeker), from Chenderoh Reservoir, Malaysia was studied from June 1991 to November 1992. A total of 329 and 246 mature females and males and 167 immature females were sampled during the study. Three breeding cycles were observed and the cycles coincided with high reservoir water level which resulted in the floodings of the littoral zone. Five and four gonad developmental stages were observed for females and males, respectively. Oocyte diameter distribution study indicated the species was a total spawner although clutches of ripe oocytes might be released over an extended time period. Fecundity was related to body weight and both absolute and relative fecundity increased with body size. Absolute fecundity ranged from 26962 ± 1484 to 173520 ± 127420 eggs fish^–1, whereas relative fecundity ranged from 121 ± 53 to 451 ± 259 eggs g^–1 body weight, respectively.     

Disproportionate allocation of mineral nutrients and carbon between vegetative and reproductive structures in Banksia hookeriana

We compared above-ground allocation patterns in mature shrubs of Banksia hookeriana from three 13-year-old populations, growing on nutrient-impoverished sands to determine whether C (dry mass) could be a substitute for mineral nutrients (N, P, K, Ca, Mg and NA). The percentage of reproductive structures to total above-ground growth (reproductive effort; RE) was integrated over nine successive reproductive cycles. Only 0.5% of above-ground dry mass was allocated to seeds compared with 31% to total RE. Allocations of N (24%) and P (48%) to seeds, and N (44%) and P (65%) to RE were much higher. Allocations of K, Ca, Mg and Na to seeds (<1–3%), and RE (21–35%) were closer to that of dry mass. Relative allocation (RA) is defined as the proportion of a nutrient element allocated to a structure relative to its dry mass. RA of P to seeds was 91 and N was 44, but for K, Ca, Mg and Na ranged from only 6 for K to<1 for Na. Thus P, and to a lesser extent N, provide a much more sensitive measure of the relative cost of reproduction than C in this nutrient-limited system.     

Demography,genealogy and genetics. The reproductive process in the populations of two French Mountain Valleys from the seventeenth to the twentieth century

An exhaustive analysis of registers of births, deaths, and marriages is used to reconstitute genealogies, both ascending and descending, for all individuals who lived in two mountain valleys: the Valserine valley (in the French Jura), which is studied from the end of the seventeenth century to the present, and the Vallouise valley (in the French Alps) studied from the seventeenth to the nieteenth centuries. This genealogical approach makes it possible to trace the reproductive process in the populations whose members lived in the valley for several generations. The Vallouise valley forms an important demographic isolate; nearly 98 per cent of those born between 1820 and 1849 were descendants of ancestors who had lived in the valley two centuries earlier. By contrast, there has been continuous immigration into the Valserine valley, which has resulted in a constant renewal of the gene pool. Only 18 per cent of the gene pool of individuals living in this valley two centuries later was contributed by those who lived in the valley and who were born before 1750.     

Sex allocation in a simultaneous hermaphrodite, the zebra goby Lythrypnus zebra: insights gained through a comparison with its sympatric congener, Lythrypnus dalli

Synopsis The sexual pattern of the zebra goby Lythrypnus zebra, is an apparent exception to sex allocation theory. Most L. zebra are simultaneous hermaphrodites (i.e., have active female and male gonadal tissue), yet it appears they do not reproduce as males and females simultaneously. Understanding the maintenance of simultaneous hermaphroditism in L. zebra could expand sex allocation theory. In this study, I used a comparison with the blue-banded goby, Lythrypnus dalli, a sympatric congener with a qualitatively similar sexual pattern, to investigate the role of male spawning rate, body size and sexual flexibility in determining the sexual pattern of L. zebra and to isolate differences between the species that might explain their differing sexual patterns. Using field measurements of male nesting success, I found no differences between the species in the body size of nesting males suggesting that large size is associated with successful male reproduction in both species. In addition, nesting males spawned at approximately three times the rate of females in both species; thus, reproduction via male function can be equally advantageous relative to adopting the female role. However, the nest longevity of L. zebra males was shorter than that of L. dalli males, suggesting reproduction via male function may be less reliable in L. zebra. Finally, under laboratory conditions, L. zebra females tended to prefer large mates, and L. zebra were able to re-allocate in both directions, exhibiting a greater capacity to switch than L. dalli. Given these results, I suggest that switching between the sexes plays a greater role in maintaining simultaneous hermaphroditism in L. zebra than L. dalli, perhaps because male reproduction is not as consistent in L. zebra. Sexual flexibility may be an important factor affecting patterns of sex allocation, generally.     

Aspects of the reproductive biology of the concha wrasse, Nelabrichthys ornatus, at Tristan da Cunha

Synopsis The reproductive biology of the concha wrasse, Nelabrichthys ornatus, at Tristan da Cunha in the South Atlantic Ocean is described. Histological evidence shows that the species is a monandric protogynous hermaphrodite. N. ornatus displays full permanent sexual dichromatism with all males occurring in the upper size classes of the population. Size specific habitat preference is described. Aspects of the mating system of the species resemble a lek although the possibility of mating site selection by females is not discounted. Spawning groups have a sex ratio of between 4 and 7 females per male.     

Reproductive responses of Iphiseius degenerans and Neoseiulus teke (Acari: Phytoseiidae) to changes in the density of the cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae)

We assessed the reproductive responses of adult female Iphiseius degenerans and Neoseiulus teke to increasing density of three stages of their prey, Mononychellus tanajoa, on cassava leaf discs under laboratory conditions. The oviposition rates increased with number of prey consumed per predator per day with a maximum of approximately two eggs per day for I. degenerans and four eggs per day for N. teke. The oviposition rate of N. teke was higher when consuming eggs than other prey stages. Neoseiulus teke was more efficient than I. degenerans in converting consumed prey into egg production. The data were adequately described by simple mathematical models.     

Behavioral and hormonal aspects of reproduction in captive goeldi’s monkeys (Callimico goeldii) in a comparative and evolutionary context

The fate of most nonhuman primate species is intimately related to man. The increasing encroachment on the natural habitat has resulted in the decimation and even near extinction of some species. Along with this development, the basic concept in many modern zoos has changed from one of merely display to self-perpetuating units. Primate research facilities are orienting their research programs towards reproductive physiology and behavior in an effort to provide basic knowledge of reproduction in these species. This increased emphasis in the area of reproductive biology and the various efforts to improve breeding of these mostly endangered primates in captivity has stimulated the author to write this review. It represents an attempt to provide the reader with basic background information relating to the endocrinology and behavior of reproduction in the clawed New World monkeys as it exists at the time of publication. The intermediate evolutionary position ofCallimico goeldii between the clawed New World monkeys and the ‘true New World monkeys’ and our relatively poor knowledge about reproduction and behavior in this particular species fully justifies the focus on Goeldi’s monkey in this essay. This review is an attempt to provide a brief history of previous studies but also the basis for research in the future. The current status of knowledge of the small-bodied clawed monkeys is also discussed in an evolutionary context, with an emphasis on the different reproductive strategies in this dynamic group of primates. The outcome, not surprisingly, confirms the unique position ofCallimico goeldii in its social, ecological, and evolutionary environment.