Non-reproductive State Research Articles

Phenology of Empoasca fabae (Harris) (Homoptera: Cicadellidae) in its Overwintering Area and Proposed Seasonal Phenology

It has been hypothesized that Empoasca fabae (Harris) lacks specific adaptations for surviving temperate zone winters, but recent findings suggest otherwise. Observations indicating that E. fabae passes winter in reproductive diapause motivated a reevaluation of E. fabae phenology. Ovarian dissections revealed that no overwintering females collected from Louisiana in mid-January 1991 had mature oocytes, whereas 65% of females collected in late February did. Field-collected females were held in the laboratory under 4 different combinations of photoperiod and temperature. Among females collected in mid-January, short day lengths and low temperatures helped maintain a nonreproductive state. Most females collected in late February began laying eggs within 3 wk, regardless of photoperiod or temperature, indicating that diapause was broken in field populations between mid-January and late February in 1991. Overwintering E. fabae were found on a variety of native evergreen plants, especially pines, over an area roughly approximated by the southern pine region, and also on a variety of primarily exotic herbaceous legumes in areas near the Gulf Coast. Repeated surveys of various sites in 1992 indicated that reproductive maturation of overwintering females occurred in mid- to late February, as the population shifted from evergreens to legumes and celtain deciduous trees, on which spring generations were initiated. The results of this study, viewed in conjunction with previous works, suggest that E. fabae is well adapted to native conditions in temperate North America, and that its phenology includes a return migration to overwintering areas.

Induction and reversal of the non‐reproductive state in winter flounder, Pseudopleuronectes americanus Walbaum, by manipulating food availability

Reversal of the non‐reproductive slate of winter flounders was induced by improved feeding.

Energy Models for the Common Vole Microtus arvalis: Energy as a Limiting Resource for Reproductive Output

A mathematical model for energy requirements of individual, non-reproducing and reproducing female small rodents is developed. Employing data on the metabolism of the common vole Microtus arvalis during reproduction, the parameters are estimated by least square techniques. In all measurements applied the temperature was held constant at 20'C. The best mathematical representation of the data is found by analysis of variance and error-term analysis. The models so found are concluded to represent the data without systematic deviations. The analysis indicates, however, that some predictive variable other than weight, number of days from conception, and number in each litter is needed to predict the metabolic rate more accurately. Such identification represents an important bioenergetic field of study. The deductions of precise mathematical functions representing the data facilitate a detailed analysis of how metabolic rates depend on weight of mother, time in reproductive period, and number of young per litter. The conclusions reached are: (1) During gestation total metabolic rate is not increased greatly relative to non-reproductive state; (2) The increased total energetic cost due to pregnancy decreases with increasing initial weight of mother; (3) An initial drop in total metabolic rate during the first 1/3 of pregnancy is observed; (4) During lactation a marked increase in metabolic rate is seen, although no marked change occurs just at the time of parturition. These conclusions are compared with earlier statements in literature. Survival of fetuses and sucklings is discussed on the basis of the bioenergetic cost due to reproduction: This indicates that energy might be a limiting resource for demographic features such as survival.

Consumption of Herbaceous Vegetation and Water During Reproduction and Development of Merriam's Kangaroo Rat, Dipodomys merriami

Field data collected from a population of kangaroo rats, Dipodomys merriami, revealed that consumption of green vegetation is correlated with lactation but not the earlier stages of reproductive activity. This suggested that herbaceous vegetation plays a minor role in initiating reproduction but plays a major role in providing support for lactation. To evaluate the requirements for water during preand postnatal development, food and water intakes of female Merriam's kangaroo rat were measured in the laboratory during the nonreproductive state, during gestation, and during lactation. Nonreproductive and gestating females both consumed an average of 4.8 g water per day. During gestation growth rates are low, and water losses are probably of the same magnitude as in nonreproductive adults. Thus, water requirements during gestation would be similar to those during the nonreproductive state. Water intake increased markedly during lactation, averaging 10.7 g per day. Food intake increased to support the energy demands of growth. Thus, water intake derived from the catabolism of food increased as well. However, the majority of the increase in water intake resulted from increased consumption of carrots, which contained abundant free water. During lactation, nursling growth was supported at an average rate of 2.1 g water per day per nursling; the minimum support required is probably somewhat less. Two females were able to successfully wean a single nursling apiece while consuming water at about the same rate as nonreproductive females and with no demands on the body stores of the nursing mothers. Except in some cases of small litter size, sources of free water (e.g., herbaceous vegetation) are necessary for successful weaning of kangaroo rat nurslings.