The Control of the Reptilian Gonad

In reptiles, there is adequate evidence to indicate environmentalcontrol of the ovarian cycle through hvpothalamic pathways andthe subsequent release of tropic hormone (s) from the anteriorpituitary. The role of the pineal-parietal complex still remainsto be elucidated. In the hypothalamus there appear to be steroidsensitive areas and both progesterone and estrogen appear tohave important feedback influences upon gonadal growth ovulation,and ovarian steroid production. Cytological studies of the reptilianpituitary indicate similar cell types to those observed in mammalianpituitaries, but thus far, two gonadotrophs cannot be identifiedwith any certainty. Chemical and biological studies of the actionof mammalian gonadotropuis suggest that in reptiles hormoneswhich are FSH-like in mammals are able to stimulate gonadaldevelopment, ovulation, and steroid biosynthesis under certainconditions. Preliminary studies of the chemistry of turtle gonadotropuishave so far demonstrated only one active principle, which ischemically similar to mammalian LH, but is far more active thanthe latter hormone in reptilian systems. Further, the hormonealso has FSH-like activity in the reptile. Thus reptilian gonadaldevelopment can be stimulated by treatment with a variety ofmammalian gonadotropins. Recent studies have indicited an importantrole for growth hormone, acting in concert with gonadotropinand estrogen in the regulation of vitellogenesis and ovariangrowth. Piolactin appears to be an antigonadal agent in reptiles,as does progesterone. The exact manner in which these hormonesexert their antigonadal action remains to be clarified, butat least one site of action is the central nervous system; othersites maybe the liver and the fat depot. Ovarian tissue from reptiles is able to synthesize and secretesteioid hormones by pathways similar to those present in mammalianovaries. Circulating levels of estrogen have not been measured,but progesterone levels in the blood show distinct changes assocntedwith pregnancy and the presence of corpora lutea in the ovary.     

Utility of a set of microsatellite primers developed for the massasauga rattlesnake (Sistrurus catenatus) for population genetic studies of the timber rattlesnake (Crotalus horridus)

I tested six microsatellite DNA primer pairs developed for the massasauga rattlesnake (Sistrurus catenatus) on a sample population of the timber rattlesnake (Crotalus horridus). It had been speculated in a previous publication that cross‐species amplification would not be worthwhile across the two rattlesnake genera. However, for this primer set (the only one currently published for the genus Sistrurus), successful amplification at each locus was accomplished for all loci with an annealing temperature of 57 °C and locus‐specific buffer conditions. Each locus was polymorphic, with the number of alleles per locus ranging from two to 12. Significant heterozygote deficits were detected for three loci (Scu01, Scu05 and Scu07). For Scu01, all individuals were homozygous for the same allele except one female who was homozygous for a different allele. This same female was also homozygous for a rare allele at Scu07. When this female was removed from the data set, the number of observed heterozygotes at Scu01 and Scu07 did not differ significantly from random expectations. However, a large heterozygote deficit persisted at Scu05 (despite subsampling), suggesting that this locus may not be useful for population genetic studies of timber rattlesnakes. Despite some limitations, this set of primers may be a useful complement to those already developed for the genus Crotalus. Moreover, the results of this study seem to provide new justification for further studies of cross‐species amplification of microsatellite loci across the two rattlesnake genera.     

Nutrient limitation of Myriophyllum spicatum growth in situ

SUMMARY. 1. The hypothesis that the submersed macrophyte biomass in natural weedbeds is nutrient limited was tested in situ by an enrichment experiment.
2. The response of Myriophyllum spicatum was significant and positive for N-enrichment, resulting in a 30–40% increase in biomass over controls. There was no response to phosphorus or to potassium enrichment.
3. Plant length and number of shoots per rephcate were also significantly increased by nitrogen additions but again showed no response to phosphorus and potassium.
4. Water depth differences were also found to affect the plant responses in some cases.
5. The macrophyte response to fertilization was similar to that recorded for emergent macrophytes and terrestrial crops but much smaller than for phytoplankton.     

The biology and life cycles of Lipsothrix spp. (Diptera: Tipulidae) inhabiting wood in Western Oregon streams

SUMMARY. 1. The immature stages of the craneflies Lipsothrix nigrilinea and L. fenderi are spent in galleries within decayed red alder ( Atntts rtibra ), in low order streams of the Pacific Northwest. L. fenderi also occurs in some coniferous wood and wood in semi-terrestrial sites at stream margins. Larvae of both species feed on the wood and are important degraders of this material.
2. The immature stages are briefly described and behaviour of the two species is compared.
3. L. nigrilinea has a predominantly biennial life cycle. It emerges from April to August in response to receding water level. The absence of this cue results in an extension of the life span to 3 or more years. The non-deterministic life cycle results in high variability of juvenile and adult weights.
4. L. fenderi is basically a biennial species, with a more synchronized autumn emergence. A portion of the population may emerge after 1 year if oviposition occurs early enough to allow autumnal growth of larvae or if growth is relatively rapid.
5. The extended life cycle of Lipsothrix spp. and the broad emergence of L. nigrilinea are concluded to be adaptations to a habitat/resource which is relatively stable and allows long-term association.     

Field evaluation of the response of Aedes albopictus (Stegomyia albopicta) to three oviposition attractants and different ovitrap placements using black and clear autocidal ovitraps in a rural area of Same,Timor‐Leste

Known oviposition attractants or stimulants were compared, singly and in combination, using inexpensive autocidal ovitraps designed to trap emerging adults, in a rural area of Timor‐Leste during the dry season. In this area, the dengue vector Aedes albopictus (Stegomyia albopicta) Skuse (Diptera: Culicidae) was abundant, but Aedes aegypti (Stegomyia aegypti) L. was not detected. The attractants were: (a) a compound found in Aedes eggs (dodecanoic acid); (b) components of nitrogen, phosphorous and potassium‐based (NPK) fertilizer, and (c) infusions of discarded cigarette butts. A solution of ammonium phosphate and potassium nitrate was significantly more attractive to gravid Ae. albopictus than water only. Dodecanoic acid and cigarette butt infusions were not significantly more attractive than the control; however, they attracted various other Diptera and many non‐culicid larvae developed in ovitraps in which these substances were used; thus, the presence of eggs or larvae of other species may have deterred Aedes oviposition. Significantly more Aedes eggs were found in ovitraps under vegetation than in ovitraps placed inside houses or against external walls. Clear‐sided ovitraps in which black mesh was placed over a black ring floating on the water surface collected significantly fewer eggs than black ovitraps with identically placed mesh and rings.