October January Research Articles

Reproduction in the lizard Mabuya heathi (Scincidae): a commentary on viviparity in new world Mabuya

The tropical Brazilian skink Mabuya heathi is viviparous, producing ova which increase in wet mass by 53 800% and in dry mass by 38 400% during gestation. Ovulation occurs during October–January, rapid growth in embryos takes place during June–October, and parturition occurs in September–November, between 9 and 12 months after ovulation. Female and male reproduction is cyclic and is synchronous between the sexes. Brood size is 2–9 [Formula: see text] and is significantly correlated to female size. Fat bodies of females are largest when embryos are small, and decrease in mass as embryos increase in size. Testes in males are largest during September–February, associated with a decrease in fat body size. Mabuya heathi is the second species of lizard in the caatinga herpetofauna shown to be strongly cyclical in reproduction and to reproduce only once per year.

Environmental characteristics of the Mandovi-Zuari estuarine system in Goa

Two rivers, the Mandovi and the Zuari, with their interconnecting canal, form an estuarine system in Goa on the west coast of India. Physical, chemical and biological features of this estuary are adapted to a seasonal rhythm induced by the annual cycle of the monsoon. Heavy precipitation and land runoff from June to September bring about large changes in temperature, salinity, flow pattern, dissolved oxygen and nutrients when the estuary becomes freshwater dominated. The monsoon season (July–September) is followed by a recovery period during the post-monsoon season (October–January) and thereafter a stable period of the pre-monsoon season (February–May) when the estuary becomes marine dominated. During the pre-monsoon (dry) season, the water in the estuarine system remains well mixed and the intrusion of salt water is felt as far as 65 km upstream in both the rivers; but during the monsoon season the rivers become stratified and a salt wedge is formed in each river which extends up to about 10 km upstream in the Mandovi and 12 km in the Zuari. The flow of the estuarine system is regulated by the entry of seawater with the incoming tide through Zuari which reaches Mandovi through the canal. The flow is reversed during the outgoing tide when the estuarine system is flushed. Dilution factors in both the estuaries are similar and vary from 1·2 to 8; highest values occur during the pre-monsoon season. Two shoals/sand bars occur permanently in Mandovi (Aguada Bay) close to a ramp-like inlet to the sea. This inlet poses no navigational problems for about 9 months during the dry season; but for a 3-month period during the monsoon, the waterway becomes hazardous and is closed to boat traffic. Heavy swell and intense wave activity lead to the transfer of sediments into the navigational inlet and the calm season brings the materials back to their original position with practically no overall change in the bathymetry of the bay. The oxygen cycle in the estuarine system is closely related to seasonal changes in temperature and bears an inverse relationship with salinity. In both the estuaries, the sulphate/chlorinity relationship remains uniform and similar to that of the sea except during the monsoon months when the relationship gets disturbed. Changes in phosphorus, nitrogen and silicon are largely regulated by rainfall and land runoff. There is no significant difference in the phytoplankton counts between Mandovi and Zuari which follow a rhythm similar to that of nitrate. Zooplankton biomass is higher in Zuari because of its greater marine influence. No seasonal variation was observed in the density of microflora in the two rivers. Bacterial counts were higher in the lower reaches of the estuarine system and decreased upstream. From its environmental features, the estuarine system can be classified as a tide-dominated coastal plain estuary.

The reproductive biology of the dab Limanda limanda (L.) in the North Sea: Seasonal changes in the ovary

Oogenesis in the dab is described in six easily identifiable stages: oogonium (Stage I), primary oocyte (II), primary vitellogenesis (III), secondary vitellogenesis (IV), tertiary vitellogenesis (V) and hyaline oocyte (VI). The annual reproductive cycle in female dab may be divided into four morphologically and histologically distinct periods: prespawning (October–January), spawning (February–April), postspawning (May–June) and resting (July–September) period.

Food and spawning activity ofCaranx hippos(L.) off the coast of Ghana

Summary Feeding and spawning activity of Caranx hippos (L.) was studied in off-shore waters and some lagoons in southern Ghana. The food of adult Caranx hippos was found to be predominantly Engraulis guineensis (Cuv.) followed by Sardinella eba (Cuv.). The food of juvenile Caranx hippos was either small fish of the species Epiplatys sexfasciatus (Stein) or the juveniles of caridian shrimps, Macrobrachium spp., or peneid shrimps, Peneus duorarum (Burkenroad). The availability of the food in lagoons is inversely correlated with the height of the water. Digestion in the adult was found to be so fast that within 4 to 5 hours the food loses its identity. Availability of food appeared to determine the distribution of Caranx hippos. Both adult and juvenile fish were found to feed mostly during the day. There appears to be protracted spawning with most activity taking place between October and late January. Ripe fish, however, were rarely encountered. Juvenile Caranx hippos were present in the lagoon all the year round with minor variations in their abundance, depending on the overall water level.

Seasonal sex skin coloration and hormonal fluctuations in free-ranging and captive monkeys

Seasonal hormonal and sex skin coloration peaks were found to be synchronized in free-ranging, socially enclosed, and individually isolated rhesus monkeys of both sexes. These occurred during the October–January mating season on La Cueva island, Puerto Rico. Individually isolated females displayed a mid-cycle peak in sex skin coloration during the period of regular cycles (September–April). Females who became pregnant during the mating season did not show the significant sex skin coloration decrease seen in nonpregnant females during the months that follow the mating season. Environmental cues, perhaps acting on a seasonal biological clock rather than social factors, are thought to be mainly responsible for the synchronous seasonal fluctuations observed. The technique used for assessing changes in sex skin coloration is shown to be an effective and reliable method for recording seasonal and intramenstrual variations of sex hormones in free-tanging and captive rhesus monkeys. Furthermore, the procedure may prove useful in studies relating behavior with sex endocrines.

Seasonal population changes of Physaloptera maxillaris (Nematoda: Physalopteroidea) in striped skunk (Mephitis mephitis).

The stomachs of 162 (89%) of 183 striped skunk (Mephitis mephitis) collected in the area of Guelph, Ontario, between September 1973 and August 1974 were infected with Physaloptera maxillaris. Adult worms were most abundant in midsummer (June–July) and rare in winter (December–March). Third-stage larvae were most abundant in late fall and midwinter (October–January) and least abundant in midsummer (June–July). Fourth-stage larvae were most abundant in spring (April–May) and least abundant in early fall (August–September). It is suggested that adults appear mainly when skunk are feeding regularly in spring and midsummer. Third-stage larvae acquired in late summer and fall fail to develop (probably because of inadequate food consumption by skunk) and persist over the winter. In spring when skunk start to feed again, overwintering larvae grow into adults and initiate the annual cycle in skunk and intermediate hosts.

The natural history of the Hardangerfjord

On the basis of a 13 months phytoplankton survey of Hardangerfjorden, south-west Norway, and the coastal waters Outside (Braarud et al. 1974), the discrepancy between the quantitative phytoplankton cycle whithin the fjord and that of the offshore area from autumn to early spring is discussed. Low light supply, small Zooplankton populations, and low phosphate concentrations within the upper 30 m layer characterize the period October–January for the fjord area. A pronounced Skeletonema costatum maximum in October–November in the fjord had no counterpart offshore where an extreme diatom scarcity prevailed. The degree of exposure to wind, through its effect upon vertical transport of the plankton algae, was found to be a main cause of this difference. This applies also to the time difference of 3–4 weeks between the advanced spring diatom maximum in the fjord and that offshore. Low grazing activity appears to be an essential prerequisite for the occurrence of large diatom populations in the fjord in ...

Physico‐chemical features of lake Pupuke, Auckland

Summary Lake Pupuke, situated in the North Island of New Zealand near Auckland (Latitude 36° 53'S, Longitude 174° 52'E), is a small, circular body of water (maximum width 1.2 km, maximum depth 55 m). From November 1966 to November 1967 observations on its physico‐chemical factors were made twice monthly. The range of temperatures in the year was 12.0–24.2°c at the surface and 11.3–14.5°c at 40 m. A thermocline farmed between early October and early January, when it became strongly developed at about 17 m and persisted until late April. Between early May and late June the stratification was breaking down and between mid July and mid September the lake was isothermal. The values for light transmitted per metre through the water were high from mid August to mid December (53–76% per metre), very low from mid December until mid February (23–49% per metre), high in March (75% per metre) and relatively constant over the winter months (53–64% per metre). The amount of light transmitted depended closely on the den...