The determinants of sexual segregation in the scalloped hammerhead shark,Sphyrna lewini

Synopsis Female scalloped hammerhead sharks move offshore at a smaller size than do males to form schools composed primarily of intermediate size female sharks. This movement results in smaller females feeding more on pelagic prey than do males and with greater predatory success. It is contended that this change in habitat causes females to grow more rapidly to reproductive size. Intermediate size females grow at a more rapid rate than males. Female scalloped hammerhead sharks mature at a size larger than males. For many elasmobranch species, females: (1) occupy a different habitat, (2) grow more rapidly prior to maturity and continue growth following maturation, (3) feed on different prey with increased feeding success, and (4) reproduce at a size larger than males. It is suggested that female segregation increases fitness, resulting in more rapid growth for the former sex. The females reach maturity at the larger size necessary to support embryonic young, yet similar age to males, matching the female reproductive lifetime to that of males.     

Comparative gastrointestinal morphology of the Kori bustard and secretary bird

Two secretary birds and three Kori bustards were studied to determine differences between their body size and gastrointestinal morphology. Body measurements were made on captive, live birds and gastrointestinal measurements on fresh postmortem specimens. For predator species, such as the Kori bustard and secretary bird, body size is a function of their ability to capture and destroy prey. While the secretary bird was clearly the taller of the two species, superior body weight, wing length, and therefore body size was noted for the Kori bustard. The size and length of the gastrointestinal tract varied between species. The secretary bird had the shorter, less complex digestive tract, with a foregut well adapted for consumption of large quantities of flesh. The large intestine was devoid of ceca. The gastrointestinal tract of the Kori bustard was markedly different from that of the secretary bird. The foregut was less complex and the large intestine possessed large, voluminous ceca.     

Leaf size and inflorescence size may be allometrically related traits

Summary Corner's rules for plant form relate the degree of branching to branch diameter, and branch diameter to leaf or inflorescence size. We report the first interspecific test of these rules for inflorescence size and branch diameter. We derived a simple corollary of Corner's rules; since leaf size and inflorescence size are both correlated to branch thickness, they may be correlated to each other. This corollary holds for Leucadendron and Protea (Proteaceae), and in certain other taxa in the Asteraceae, Bruniaceae and Pinaceae which also have leaves and reproductive structures on the same shoot. For such taxa this implies that selection for aspects of floral display (inflorescence size, pollination type) may also be expressed at the level of leaf size and vice versa. This has implications for many aspects of botany and also points to the importance of the co-ordinating role of plant architecture for aspects of plant form.     

Effects of flowering plant's patch size on species composition of pollinator communities,foraging strategies,and resource partitioning in bumblebees (Hymenoptera: Apidae)

Summary In 4 common Middle-European mainly bumblebee-pollinated plant species (Impatiens glandulifera, Echium vulgare, Aconitum napellus, Symphytum officinale) the influence of patch size on species composition of the pollinator community was studied. Short-tongued species were most dominant in large patches, while small patches were frequented by middle- and long-tongued bumblebees. This phenomenon was extremely obvious in Symphytum officinale and Aconitum napellus, where short-tongued species had bitten a hole in nearly every flower of large patches. Long-tongued species were forced to small patches, where nectarrobbing occurred only exceptionally. In small patches visitationrate (Number of visits per flower per hour) was not lower but either equal or even higher then in large patches. Nectar measurements in Echium vulgare showed, that not only the mean quantity of nectar but also the variance was lower in small patches. As a result, the possible gain can be predicted much more precisely in a small patch than in a large one, and bumblebees have less difficulties in making the right foraging decisions. According to this, foraging strategies depend on patch size. This was confirmed by a computer simulation. The conclusion can be drawn, that many bumblebee species are able to share the same resource by using different patch sizes. Since large flower patches occur mainly in man-made habitats, the dominance of short-tongued species in many bumblebee communities studied by other authors may be unnatural.Supported by the Landesgraduiertenförderung Baden-Württemberg     

Effect of selection intensity and population size on percent oil in maize,Zea mays L

Summary The effect of selection intensity and population size on the response to selection for percent oil in the grain of maize (Zea mays L.) was evaluated in a replicated experiment over ten cycles of selection. An open-pollinated variety, Armel's Reid Yellow Dent, was divided into subpopulations of 6,10 and 50 plants. Selection proportions of 17% and 5% were imposed upon each subpopulation. Selection was based on the percentage of oil in individual kernels as determined by wide-line nuclear magnetic resonance spectroscopy. As expected, total response to selection increased with larger population sizes and selection intensities. The concave shape of the response curves suggested that an appreciable part of the genetic variance can be attributed to additive genes at high initial frequencies, dominance genes at low initial frequencies, or to the generation of negative linkage disequilibrium due to selection. The consistently greater loss of vigor experienced by the more intensely selected populations reflects the enhancement of inbreeding due to artificial selection, an effect that increases with the intensity of selection. The results indicate that combined selection, based on kernels and using within- and amongfamily information, will be more efficient than other conventional selection procedures, including the normal combined scheme where selection is based on plants.Deceased     

Egg weight, batch size and fecundity of the spotted stalk borer, Chilo partellus in relation to weight of females and time of oviposition

The egg laying pattern of the spotted stalk borer on sorghum and maize, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) was studied during the first three nights of oviposition under laboratory conditions. More than 50% of both eggs and egg batches are laid during the first night of oviposition. Batch size decreases with time, whereas mean egg weight remains constant.Larger females lay both larger eggs and egg batches than smaller ones. They are also more fecund but it is only the second night of oviposition that contributes significantly to this difference.The reproductive effort decreases much with time. Allocation of reproductive reserves to early eggs seems more important than having eggs evenly distributed over time. Larger females use proportionally more resources to the production of late eggs. Large eggs are likely to contain more yolk which could be of importance for the ballooning behaviour of newly hatched larvae.

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Résumé La ponte de C. partellus Swinhoe a été étudiée au laboratoire pendant les trois premières nuits de la ponte. Plus de 50% des ooplaques et des oefs ont été pondus pendant la première nuit. La taille des ooplaques diminue avec le temps, tandis que le poids moyen des oeufs reste constant.Les grosses femelles pondent des ooplaques et des oeufs plus grands que les petites. Elles sont aussi plus fécondes, mais c'est seulement à la seconde nuit de ponte qu'est due cette différence.Le reproduction diminue beaucoup avec le temps. L'affectation aux premiers oeufs des réserves utilizées pour la reprodution semble plus importante que l'émission d'oeufs régulièrement répartis dans le temps. Les grosses femelles utilisent proportionnellement plus de ressources à la production d'oeufstardifs. Les gros oeufs contiennent vraisemblablement plus de vitellus que pourrait être nécessaire pour le comportement aérostatique des chenilles néonates.

     

Odontometric profile of a prehistoric southeastern Florida population

This study analyzes and compares the dental size variation and sexual dimorphism of the Highland Beach Mound people, a late southeastern prehistoric aboriginal Florida population (ca. 800-1200 AD) with a somewhat earlier midwestern group (ca. 200-800 AD) and an Archaic sample (ca. 4160-2558 BC). The lengths and breadths of maxillary and mandibular permanent teeth of 99 individuals were measured, and crown surface areas were calculated for the molars. Results indicated that there was little sexual dimorphism. Only the mesiodistal dimensions of the upper P2 and lower C were significantly different at the P less than 0.05 level. In terms of dental size, what appears to be a chronologically based reduction in most points of comparison was seen in all three groups, with the exception of the molars, which were larger in the Highland Beach sample than in the earlier Schultz Mound.     

Effects of crayfish size,orientation, and movement on the reactive distance of largemouth bass foraging in clear and turbid water

Laboratory experiments were performed in clear and turbid water to determine the effects of prey size, orientation, and movement on the reactive distance of largemouth bass (Micropterus salmoides) when feeding on crayfish (Procambarus acutus). In clear water, the reactive distance increased linearly with an increase in prey size, and prey movement resulted in a significant increase in the reactive distance. Prey orientation (head-on versus perpendicular) did not change the reactive distances. In moderately turbid water, the reactive distance did not increase with increased prey size, and prey movement did not result in any changes in the reactive distance. The absence of any effects of prey orientation in clear water or prey movement in turbid water is inconsistent with results from studies using different species (primarily planktivorous fish). I propose that largemouth bass change their foraging tactics as prey visibility changes. When prey are highly visible (low turbidity), predators attack (react) only after prey recognition, which is based on multiple cues such as prey size (length, width) and movement. When prey are less visible (high turbidity), predators attack immediately upon initial prey sighting, which does not depend on prey size or movement.     

Benthic algal response to N and P enrichment along a pH gradient

Nutrient enrichment and its effect on benthic algal growth, community composition, and average cell size was assessed across two sites of differing pH within a single habitat. Nutrients were added using in situ substrata, which released either N, P, or no additional nutrients (controls) at each site for 21 days. Upon collection, chlorophyll and biovolume standing stocks of the attached algal microflora were measured. Chlorophyll concentration was different among all treatments, accumulating greatest on P, followed by N, and the least on C substrata (P < 0.001) and was highest at site-2 (P < 0.001), while total algal biovolume was highest on P compared to both N and C substrata (P < 0.05) and did not vary between sites. Increased growth on P substrata was due to the enhanced biovolume of filamentous green algae, although the affected taxa varied between sites. Biovolume to cell density ratios (as a measure of average cell size) were highest on P substrata over both N-enriched and control substrata (P < 0.05) and this pattern was similar between sites. Progression towards a community composed of larger cells following P enrichment observed along this pH gradient, seems to be related to the dominance of larger celled filamentous green algae. Thus, nutrients exhibited greater control on benthic algal growth than did changes in hydrogen ion concentration.Contribution number 581, Great Lakes Environmental Research LaboratoryContribution number 581, Great Lakes Environmental Research Laboratory