Different structure of polytene chromosomes ofPhaseolus coccineus suspensors during early embryogenesis

Summary The pattern of DNA and RNA puffs in pair VII of polytene chromosomes has been investigated in the suspensor ofPhaseolus coccineus during early embryo development. The pattern of³H-TdR and³H-U incorporation has been also detected. Collected data indicate that: 1. both heterochromatic regions, p₁₁ and q_(111+112), of chromosome pair VII, organize large DNA puffs; 2. DNA puffs of both regions are specific of different embryo differentiation steps; 3. a seasonal influence on the DNA puffing seems also to be present, as demonstrated by the comparison of the results collected in two different crops; 4. the incorporation experiment by³H-TdR evidences that not all DNA puffs show clustered labeling; 5. the RNA puffing of the two regions seems also to be specific of determined embryo stages.     

Precocene causes male determination in the aphid Myzus persicae

When adult apterous viviparous females of Myzus persicae, reared in short night conditions at 21–23°C, are treated with the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene, they deposit males towards the end of their reproductive lives. The first-born normal daughters of the treated females also deposit some males at various times in their reproductive lives. Karyotypic analysis was used to investigate the sequence of male and female embryos in the ovarioles of precociously metamorphosed aphids. The experiments support the hypothesis (Mittler et al., 1979) that juvenile hormone level controls the sex determination process in aphids. Since male aphids have an XO sex chromosome constitution, this implies that juvenile hormone level influences the behaviour of the X-chromosomes at or before the single maturation division of the egg. At this division one X-chromosome is eliminated from eggs which will develop as males. Aphids provide the first example of a specific endocrine influence on chromosome behaviour in sex determination.     

Effect of Aedes aegypti (Diptera:Culicidae) Age on Sex Ratios in Romanomermis culicivorax (Nematoda:Mermithidae)

First, second, third, early and late fourth-instar larvae, and pupae of Aedes aegypti were infected with Romanomerrais culicivorax and reared at 20, 25, and 30 C. An increase in the ratio of male to female nematodes was observed with increase in host age at the time of infection at each temperature. The number of pupal and late fourth-instar infections was low, but R. culicivorax continued to develop in adult A. aegypti. Since male nematodes were recovered from both male and female hosts infected as late fourth instars or pupae, the sex of the host did not influence the sex of the nematode.     

Some New Phenomena in Macronuclear Development of Euplotes patella Exconjugants

Two new phenomena were observed during macronuclear development in E. patella. During the formation of giant chromosomes, the number of chromosomes decreased while individual chromosomes gradually became longer and thicker. Immediately before macronuclear elongation, ring-like anlagen appeared, which did not contain chromatin at their centers. The course of macronuclear development in Euplotes is reconsidered in light of these findings.     

Behavioral response of 12 ungulate species in captivity to the presence of humans

Twelve species of captive ungulates were studied to determine behavioral responses to the presence of a zookeeper within the exhibit and in front of the exhibit, with and without zoo visitors present. Significant differences in behavior occurred between species for nearly all behaviors observed. A significantly greater occurrence of vigilance and approach behavior was directed toward the zookeeper while within the exhibit relative to when the zookeeper stood in front of the exhibit. A significantly lower occurrence of eating or drinking occurred when the zookeeper was inside the exhibit. Significant differences occurred across size categories in the occurrence of approaching the zookeeper. The most frequently scored behavior was visual orientation. Statistically significant differences in the occurrence of visual orientation directed by females toward the zookeeper existed across size category, with more vigilance by species with larger body size. A statistically higher occurrence of vigilance toward the zookeeper was directed by female ungulates but not by males when the zoo was closed to the public. Although no statistical significance was found regarding the intraspecific vigilance of males, data on females revealed significant differences across species and across size categories. When data regarding vigilance toward the public were analyzed, statistically significant differences existed between species for females only. Likewise, when data regarding interspecific vigilance were examined, statistically significant differences were found across size categories for females, but not for males. The potential roles of vigilance in the wild are discussed in reference to its role in captivity.     

Is male back space limiting? An investigation into the reproductive demography of the giant water bug,Abedus indentatus (Heteroptera: Belostomatidae)

Because male giant water bugs in the subfamily Belostomatinae provide parental care by brooding eggs on their back, an accurate assessment can be made of both the actual and potential reproductive capacity of males. Two operational sex-ratio (OSR) indices were developed and empirically measured for a population of giant water bug, Abedus indentatus,in California. One index was based on reproductive rates measured in the laboratory; the other index was based on reproductive resources observed in the field. Both OSR indices suggest that the operational sex ratio fluctuates between maleskewed ratios in the summer and femaleskewed ratios in the winter. This pattern appears to be the consequence of two factors. First, the adult sex ratio is significantly female biased. Second, although males can outreproduce females at high ambient temperatures, the reverse is true at low temperatures. Possible reasons for the female-skewed adult sex ratio are examined, including differential recruitment, differential mortality, and sampling bias.     

Conservatism of sites of tRNA loci among the linkage groups of severalDrosophila species

Summary The sites of seven tRNA genes (Arg-2, Lys-2, Ser-2b, Ser-7, Thr-3, Thr-4, Val-3b) were studied by in situ hybridization.¹²⁵I-labeled tRNA probes fromDrosophila melanogaster were hybridized to spreads of polytene chromosomes prepared from fourDrosophila species representing different evolutionary lineages (D. melanogaster, Drosophila hydei, Drosophila pseudoobscura, andDrosophila virilis). Most tRNA loci occurred on homologous chromosomal elements of all four species. In some cases the number of hybridization sites within an element varied and sites on nonhomologous elements were found. It was observed that both tRNA ₂ ^Arg and tRNA ₂ ^Lys hybridized to the same site on homologous elements in several species. These data suggest a limited amount of exchange among different linkage groups during the evolution ofDrosophila species.     

Molecular cloning and chromosomal location of genes encoding the “Early-methionine-labelled” (Em) polypeptide of Triticum aestivum L. var. Chinese Spring

Summary The Early-methionine-labelled (Em) polypeptide is the most abundant cytosolic polypeptide found in mature wheat embryos. Using a near full-length cDNA clone as a hybridisation probe to detect genomic sequences by Southern blotting of electrophoretic separations of genomic DNA derived from Triticum aestivum L. var. Chinese Spring and a series of its aneuploid derivatives, we demonstrate that the Em polypeptide is the product of a small multigene family in which the copies are located on each of the long arms of the homoeologous group 1 chromosomes. Screening of a variety of genotypes additionally reveals a number of restriction fragment length polymorphisms associated with these loci. Screening of a library of genomic DNA cloned in the vector EMBL 4 has resulted in the isolation of a genomic fragment containing two closely linked Em genes. These are separated by ca. 2.5 kb. Analysis of restriction enzyme digests of this clones fragment has identified it as originating from chromosome 1A.     

The social development of free-ranging infantLemur catta at Berenty reserve,Madagascar

The social development of 11 free-ranging infantLemur catta was examined over the first 16 weeks of the infants' lives. By 16 weeks, infants still occasionally suckled and were carried dorsally, but on the whole, they were independent of their mothers. Sex or mother's rank was not found to affect frequency or type of play behavior. Mother's rank had no effect on frequency of maternal rejections, from the nipple or from riding, but female infants were rejected slightly more frequently than males were. Mothers tended to reject infants more severely and more frequently from dorsal riding than from the nipple. Sex and rank differences were not found with respect to behaviors determined as measures of independence; however, lower-ranking infants engaged in significantly more dependent behaviors than higher-ranking young did. It may be necessary for the infant of a low-ranking mother to maintain closer proximity to its mother for a longer period of time during infancy because such infants may be subject to abuse by higher-ranking group members and, furthermore, may not be as readily rescued in a stressful or dangerous situation as a higher-ranking infant. Sex was not found to be a factor in terms of measures of dependence. The lack of sex differences in developmental behaviors in this species may be related to female dominance, as well as to the fact that, as adults, both sexes engage in aggressive territorial behavirs.