Analyses of growth processes of pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, through the use of daily otolith increments

It has been reported that pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, appear in small and large size groups during spawning despite being an annual fish. It is hypothesized that pond smelt have a bimodal life history, anadromous for large size groups and resident in the lake for small size groups. We calculated the body length and growth rate of the small and large size groups through the use of daily otolith increments and compared growth parameters between groups. In addition, the growth processes of resident fish in Lake Ogawara and anadromous fish in the adjacent sea were examined and compared with small and large size groups, respectively. We found that the two size groups diverged after 40–50 days from hatching with significant size groups present after 50 days. Through otolith increment analysis the growth processes of the small and large size groups were correlated with resident and anadromous forms respectively. These results revealed the utility of otolith increment analyses to clarify population structure of this species.     

Evolution of Rotifer Life Histories

When compared to most other multicellular animals, rotifers are all relatively small, short-lived and fast-reproducing organisms. However among and within different rotifer species there is a large variation in life history patterns. This review accounts for such variation in rotifers, with a strong focus on monogonont rotifers. As the life cycle of monogonont rotifers involves both asexual and sexual reproduction, life history patterns can be examined on the level of the genetic individual, which includes all asexual females, sexual females and males that originated from one resting egg. This concept has been applied successfully in many areas, for example in predicting optimal levels of mictic reproduction or sex allocation theory. The benefits and implications of the view of the genetic individual are discussed in detail. Rotifer life histories can also be viewed on the level of physiological individuals. A large part of this review deals with the life histories of individual amictic females and addresses life history traits like body size, egg size and resource allocation patterns. It asks which trade-offs exist among those traits, how these traits change under the influence of environmental factors like food availability or temperature, and whether these changes can be interpreted as adaptive.     

广大腿小蜂对菜粉蝶蛹体型大小的产卵选择及后代发育表现

产卵选择与后代发育适合度之间的相关性是进化生态学的主要科学问题之一。为探究广大腿小蜂(Brachymeria lasus)对不同体型大小寄主的选择和后代发育表现的关系,采用饥饿方法处理4龄菜粉蝶(Pieris rapae)幼虫以获得体型大小(用体质量表示)差异较大的寄主蛹,供寄生蜂选择寄生。结果表明,广大腿小蜂显著偏好体型较大的寄主蛹,而且在体型较大的蛹内产雌性后代的概率更大;子代蜂体型大小与寄主蛹大小存在显著的正相关性,但子代蜂发育历期与寄主蛹大小无相关性。研究说明,广大腿小蜂对菜粉蝶蛹的寄生选择与后代发育表现,符合寄主大小-质量模型的预测。     

Latitudinal variation in wild populations of Drosophila melanogaster: heritabilities and reaction norms

Large amounts of genetic variation for wing length and wing area were demonstrated both within and between Drosophila melanogaster populations along a latitudinal gradient in South America. Wing length and wing area showed a strong positive correlation with latitude in both wild flies and laboratory-raised descendants. Large population differences were observed for heritability and coefficient of variation of these two traits, whereas relatively small population differences were found for development time, viability, pupal mortality, sex ratio and their norms of reaction to four developmental temperatures. No clear-cut latitudinal clines were established for these life-history characters. These results are discussed in the light of Bergmann's Rule and the relation between larval development and adult body size.     

Phenotypic similarity and differentiation among sympatric cryptic species in a freshwater amphipod species complex

1. Cryptic species diversity poses evolutionary questions about its origin and maintenance, and ecological questions about the coexistence of seemingly identical species. 2. We examine patterns of morphological and life history differentiation in three sympatric cryptic species of freshwater amphipods within the Hyalella azteca species complex. These species are separated by extensive molecular evolution, but appear similar in phenotype. Species were collected from the littoral zone of a small kettle lake in Michigan, U.S.A., and identified to species by molecular genetic methods. 3. Two of the species were similar, differing only in female size, whereas the third was larger in body size and had larger clutches of smaller eggs than the other two. There were differences between the species also in pleon spine length and antennal segment number. 4. An analysis of allozyme variation among the cryptic species in three lakes suggests that the species are reproductively isolated within lakes. 5. We suggest that phenotypic similarity of these species is maintained by size‐selective predation by fish. The small, but statistically significant, differences in body size may form the axis for a tradeoff between resource exploitation and predator avoidance, a condition that can foster coexistence of phenotypically similar species.     

Embryonic and larval development of a Japanese spinous loach,Cobitis takatsuensis

The embryonic and larval development ofCobitis takatsuensis, a mountain stream spinous loach, was surveyed by incubating artificially inseminated eggs. The mean diameter of the inflated eggs and mean total length of newly-hatched larvae were 2.7 mm and 5.7 mm, respectively. The eggs were spherical, transparent and unpigmented, with a pale yellow yolk and no oil globule. The daily cumulative temperature to hatching was estimated to be 70–110°C. day. Hatched larvae were unpigmented with outer gill filaments on their cheeks, as in otherCobitis species, but the melanophores were comparatively less obvious at each developmental stage. The larvae started feeding eleven days after hatching yolk absorption being completed sixteen days after hatching. All the fin rays were fully developed and the juvenile stage reached at 16 mm TL, 38 days after hatching. Embryonic and larval developmental traits ofC. takatsuensis, such as egg size, clutch size and larval pigmentation, were similar to the Korean species,Niwaella multifasciata, that lives in the upper reaches of the Nak-tong river, andN. delicata, which inhabits Japanese mountain streams, rather than to its congeners. Among cobitine fishes, the spawning of a small number of larger eggs yielding larger larvae without pigmentation, characteristics shared byC. takatsuensis, N. multifasciata andN. delicata, is attributable to adaptation to cold mountain streams.     

Size-dependent predation risk in tree-feeding insects with different colouration strategies: a field experiment

1. Body size is positively correlated with fecundity in various animals, but the factors that counterbalance the resulting selection pressure towards large size are difficult to establish. Positively size-dependent predation risk has been proposed as a selective factor potentially capable of balancing the fecundity advantage of large size.
2. To construct optimality models of insect body size, realistic estimates of size-dependent predation rates are necessary. Moreover, prey traits such as colouration should be considered, as they may substantially alter the relationship between body size and mortality risk.
3. To quantify mortality patterns, we conducted field experiments in which we exposed cryptic and conspicuous artificial larvae of different sizes to bird predators, and recorded the incidence of bird attacks.
4. The average daily mortality rate was estimated to vary between 4% and 10%. In both cryptic and conspicuous larvae, predation risk increased with prey size, but the increase tended to be steeper in the conspicuous group. No main effect of colour type was found. All the quantitative relationships were reasonably consistent across replicates.
5. Our results suggest that the size dependence of mortality risk in insect prey is primarily determined by the probability of being detected by a predator rather than by a size-dependent warning effect associated with conspicuous colouration. Our results therefore imply that warningly coloured insects do not necessarily benefit more than the cryptic species from large body size, as has been previously suggested.     

Body size variation among mainland populations of the western rattlesnake (Crotalus viridis)

In general, squamate reptiles follow the converse to Bergmann's rule, attaining smaller sizes in cooler environments, whereas other vertebrate groups follow Bergmann's rule, attaining larger sizes in cooler areas. Intensive studies of body size evolution for species of squamates are necessary to understand the processes responsible for this trend. Here I present data on body size variation among mainland populations of the western rattlesnake, Crotalus viridis. This species consists of two well-differentiated phylogenetic clades, therefore all analyses were performed for the C. viridis group as a whole and separately for each of the two clades within the C. viridis group. Although both phylogenetic and nonphylogenetic analyses were performed, the data did not show phylogenetic conservatism, and therefore the nonphylogenetic results are preferred. I found no significant relationships between mean adult female snout-vent length and any of the physical and climatic variables that were examined for the C. viridis group using simple linear regression analysis. Examined separately, I found that individuals of the western clade, C. oreganus, were smaller in cooler and more seasonal environments, whereas individuals of the eastern clade. C. viridis sensu stricto, were larger in cooler and more seasonal areas. Thus, the observed size trends were in opposite directions for the two clades. Multiple regression analysis revealed that seasonality was a stronger predictor of body size variation than was temperature for both clades. The differences in body size trends between these clades may be due to differences in mortality rates among populations.