Some environmental factors affecting the reproduction of Aphanius dispar (Rüppell, 1828)

In order to determine the suitability of thecyprinodont fish Aphanius dispar as a biologicalcontrol agent for mosquito larvae, the effects oftemperature, salinity, feeding rate and photoperiod onits reproductive condition were studied. The factorsexamined were the gonado-somatic index (GSI) and fourdistinct stages of cell maturation in the ovaries(oogonia, primary oocytes, secondary oocytes andmature ova). The fish were found to be tolerant to awide range of the examined factors. GSI's were notaffected by ambient temperatures over the range of18 °C to 37 °C. However, oocyte maturationstages increased as temperatures rose from 18 °Cto 27 °C, with mature ova first being found at thelatter temperature. No significant differences amongmaturation stages were found between27 °C–37 °C. At salinities ranging from of0 ppt to 56 ppt, no significant differences were found betweenmean GSI's, except for the two extremes of the testrange. The ovaries of fish kept in distilled watercontained primordial germ cells only. In feedingexperiments, significant differences were found onlybetween the ovaries (GSI's and oocyte maturationstages) of fish deprived of food and those fed at1% body weight per day. Regarding photoperiod,a decrease in day length from 14L:10D (the longest dayof the year) to 10L:14D (the shortest) caused adecrease in oocyte maturation stages. Fish at theintermediate level (12L:12D) still had ovariessuitable for spawning, whereas those at 10L:14D didnot. The results of this study show that limitinglevels for adequate reproductive condition were foundfor some of the factors investigated, however, rangesof the factors above these levels were relativelylarge. That Aphanius dispar's reproductivecondition may be controlled in an artificialenvironment is essential for it to be mass produced,and a prerequisite for its use in the biologicalcontrol of mosquito larvae.     

Morphological variation in the polyps of the scleractinian coral Favia speciosa (Dana) around Singapore

A photographic technique was used to examine morphological differences in the living polyps of Favia speciosa sampled from three sites around Singapore. Eight characters were measured, seven of which differed significantly between the three study sites. Sedimentation rates and character size were much higher at the site closest to the mainland than at the two sites further from shore. Land reclamation and dredging contribute to high sediment rates in Singapore waters; these rates decrease with increasing distance from shore. Large polyps close to the main island of Singapore are possibly a plastic, or selected for, response to high levels of sediment.     

Microgeographic variation in shell characters of Littorina saxatilis Olivi—a question mainly of size?

The question of whether there are shape differences between populations of Littorina saxatilis living in different environments is examined by multivariate analyses of 13 morphological characters. Principal component analysis reveals that morphologic differences between populations from habitats with contrasting degrees of wave exposure are mainly due to a general size factor, including shell thickness. Utilizing the group structure among the snails, canonical variate analysis discloses that the main character excluding size that influences subpopulation differentiation is pointedness.     

Comparative growth in the postnatal skull of the extant North American turtle Pseudemys texana (Testudinoidea: Emydidae)

Bever, G.S. 2007. Comparative growth in the postnatal skull of the extant North American turtle Pseudemys texana (Testudinoidea: Emydidae). —Acta Zoologica (Stockholm) 88 : 000–000 Postnatal growth is one of the many aspects of developmental morphology that remains distinctly understudied in reptiles. Variation and ontogenetic scaling within the skull of the extant emydid turtle, Pseudemys texana is described based on 25 continuous characters. Results indicate that skull shape in this species changes little during postnatal growth relative to the only cryptodire taxa for which comparable datasets are available (Apalone ferox and Sternotherus odoratus). This relative lack of change results in the paedomorphic retention of a largely juvenile appearance in the adult form of P. texana. The skulls of males and females, despite the presence of distinct sexual dimorphism in size, grow with similar scaling patterns, and the few observed differences appear to reflect alteration of the male growth trajectory. Comparisons with A. ferox and S. odoratus reveal a number of similarities and differences that are here interpreted within a phylogenetic context. These preliminary hypotheses constitute predictive statements that phylogenetically bracket the majority of extant cryptodire species and provide baseline comparative data that are necessary for the future recognition of apomorphic transformations. Plasticity of ontogenetic scaling as a response to the homeostatic needs and behaviour of individuals commonly is evoked as a limitation of ontogenetic scaling as a means to inform phylogenetic studies. These evocations are largely unfounded considering that variability itself can evolve and thus be phylogenetically informative.     

Effects of phytochemical variation in quaking aspen Populus tremuloides clones on gypsy moth Lymantria dispar performance in the field and laboratory

1. This study investigated how phytochemical variation among clones of quaking aspen Populus tremuloides, growing in a common habitat, affects the growth and fecundity of a model herbivore. 2. Gypsy moth Lymantria dispar larvae were reared from egg hatch to pupation on 10 aspen clones in the field or on excised foliage in the laboratory. Foliage was collected from each clone, and concentrations of phenolic glycosides, condensed tannins, nitrogen, and water were determined. 3. Herbivore fitness parameters and aspen phytochemical concentrations varied significantly among clones. In both the field and laboratory, larvae reared on clones containing high concentrations of phenolic glycosides exhibited prolonged developmental times and reduced pupal weights and fecundity. Herbivore performance parameters were also related positively to foliar nitrogen concentrations in the laboratory. Food consumption, but neither growth nor reproductive parameters, were related positively to condensed tannin concentrations. 4. In this study, foliar concentrations of phenolic glycosides were implicated as a significant determinant of food quality for gypsy moths, consistent with results of previous laboratory experiments. Additionally, this study documents a case in which host plant variation at a local level influences the performance and possibly the distribution and abundance of an important herbivore.     

Intraspecific Morphological Variation Among Populations of Pratylenchus brachyurus and P. coffeae

Three populations of Pratylenchus coffeae and two of P. brachyurus, each originating from a single female, were maintained on Citrus spp. or Solanum nigrum L. for several years under greenhouse conditions. Nematodes were extracted from roots, and adult female specimens were killed, fixed, and mounted in glycerine for microscopic study. Variables measured were distance between vulva and anus and lengths of the stylet, posterior uterine sac, and tail. The mean data and coefficients of variability suggest that styler length had the least variability, and length of posterior uterine sac the most. When males and distinct spermathecae are not evident in P. coffeae populations, the species can he distinguished from P. brachyurus by a shorter mean stylet length, longer mean posterior uterine sac length, and much longer distance between the vulva and anus.     

Morphological variation in the palaeonemertean Tubulanus annulatus (Montagu, 1804)

Previous studies on the palaeonemertean Tubulanus annulatus have hinted on possible geographic variation, or even a species complex. This study describes the variation in morphology, focusing on the characters that have been supposed to vary geographically. Specimens from the Swedish west coast (Tjärnö and Kristineberg), Scottish west coast (Millport), and the Mediterranean (Naples and Split) were included in the study. It is concluded that the pattern of variation in the studied characters do not correspond to geography and most of the character states previously thought to vary geographically are in fact found within one and the same population.