На материалах многолетних исследований рассматриваются особенности динамики численности, пространственной и генетической структуры, изменчивости ряда морфологических показателей группировок остромордой лягушки, расположенных в черте города. Некоторые из исследованных параметров свидетельствуют о наличии адаптивных изменений в группировках, подверженных значительному антропогенному воздействию.
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194The results of long-term field studies showed that fecundity of female Rana arvalis Nilss. frogs may increase on account of an increase in their body length or, alternatively, the shortening of their hindlimbs, with body length remaining unchanged. The type of reproductive strategy is independent of the annual population dynamics, but gradually changes (toward an increased dependence on female body length) with a decrease in the overall number of frogs involved in breeding, which occurs'as the result of succession in the habitat studied. The growth of hindlimbs only, without an increase in body length, does not contribute to fecundity but is necessary for normalizing morphological proportions. Hence, fecundity and hindlimb length are the parameters "competing" for the resource provided by the female's body. In general, fecundity (F) as a function of body (L) and hindlimb length (n may be represented as F = (F,,L)/(L +j), where F,, is the maximum possible level of fecundity. Morphological proportions of females, rather than their absolute size, are the main parameters determining the dynamics of fecundity; hence, the abstract concept of sizes (as conventially used in ecology) loses its meaning in this case. Hindlimbs may be regarded as the "viability component," and body size, as the "reproductive component." Taking into account that both of these components belong to the morphological structure of the phenotype, it is principally impossible to distinguish between competition of adaptive components for some common resource and their morphogenetic interaction necessary for the maintenance of normal morphological proportions.
Although Rana dalmatina and Rana temporaria are widely distributed species throughout Europe, studies regarding the breeding biology of R. dalmatina and the long term fluctuations of the populations of these species, when they are syntopic are scarce. In this study I present data gathered during eight years, regarding the breeding activity and long term trend of two populations that reproduces in a seminatural pond. The prespawning period lasts in average 5.6 days in R. dalmatina and 4 days in R. temporaria. The male (i.e. calling) and female (i.e. spawning) activities are correlated. A significant negative correlation between the average temperature in February and the beginning of the breeding activity in both sexes of both R. dalmatina and R. temporaria populations was observed. The intensiy of the spawning is varying between the years, and is influenced by temperature. Egg masses of both R. dalmatina and R. temporaria were deposited in shallow water, close to the shore. A negative correlation was found between the number of deposited egg masses in the two species.
Using ventricular cardiomyocytes of the common frog, Rana temporaria, we investigated the metabolic strategies employed by the heart to tolerate 4 mo of hypoxic submergence (over wintering) as well as acute bouts of anoxia. In contrast to what is observed for the whole animal, there was no change in oxygen compared with those isolated from 4-mo hypoxic animals. Furthermore, cells from both normoxic and hypoxic frogs were able to completely recover oxygen consumption following 30 min of acute anoxia. From estimates of ATP turnover, it appears that frog cardiomyocytes are capable of a profound, completely reversible metabolic depression, such that ATP turnover is reduced by 190% of control levels during anoxia but completely recovers with reoxygenation. Moreover, this phenomenon is also observed in frogs that have been subjected to 4 mo of extended hypoxia. We found a significant increase in the stress protein, hsp70, after 1 mo of hypoxic submergence, which may consumption in cardiomyocytes isolated from normoxic frogs contribute to the heart’s remarkable hypoxia and anoxia tolerance and may act to defend metabolism during the overwintering period.
During our study we identified 79 prey items in the trophic spectrum of the Moor frog (Rana arvalis Nilsson, 1842) with average number of prey items per stomach – 5.27 and 100 prey items in the trophic spectrum of the Common frog (Rana temporaria L., 1758) with average number of prey items per stomach – 3.84. In both species the most important prey category is Coleoptera (Insecta). Other important prey animals are from Hemiptera, Hymenoptera and Diptera orders (Insecta) as well as non-insect invertebrates (Gastropoda, Arachnida, Myriapoda) which also play significant role. Both frogs consume almost only terrestrial prey. The trophic niche breadths for both species are quite high (Rana arvalis – 23.70; Rana temporaria – 12.25). The estimated trophic niche overlap between the species is moderate (63.5%), but the numeric proportion of all prey taxa occurring in the stomachs do not differ significantly between the species. Rana arvalis and Rana temporaria are polyphagous zoophages, like other amphibian species and they are probably consuming all mobile objects which they come in contact with and can swallow.
Geographical variation of sexual dimorphism in growth rate and body size in mature Rana arvalis collected in five distinct localities was studied by comparing body length and age. Sex-specific growth rates and the degree of expression of sexual differences in body length and age composition change from the southwest (Minsk and Chernobyl provinces) to the northeast (Kirov province). The average age was higher in females (than in males) from two northern populations, but lower in females from three southern populations. Such differences depend not only on the duration of the activity season, but also on local conditions that caused differences in female and male survival. These differences, in turn, caused differences in age at maturity, age composition of breeding females, and in their contribution to reproduction even between populations from localities with similar duration of the activity season. The reasons for relatively low growth rates and relatively high survival in males from southern populations remain unclear.
A long-term study (1987–2007) on a Rana arvalis population in Moscow province focused on body length of males and females, and age-dependent reproductive characteristics. Correlations between egg diameter and reproductive effort with female body length weakened with age, whereas the relationship between body length and fecundity was characterized by positive allometry. Significant directional interannual changes in body length and reproductive characteristics paralleled with a relative decrease of the mature part of the population. The survival of mature females and males depended on premetamorphic survival, and was higher in earlier study years characterized by more favorable conditions in the aquatic phase. A decrease in net reproduction rate (R0) and, therefore, a limitation of population growth, was revealed both at relatively high and low levels of initial cohort size. The increase in the estimated recruitment exerts a strong influence on R0 via the decrease in the premetamorphic survival and, to a lesser extent, via a decrease in body length and fecundity of three- and four-year-old females. Changes in the annual number of breeding females were rather abrupt; however, a general long-term tendency for a decrease in female numbers was observed from 1992 to 1998, and the numbers remained low until present. The main reason for this decrease was a considerable deterioration of premetamorphic conditions, i.e. a decrease in carrying capacity of the aquatic environment. Sexual dimorphism in body length and growth rates (males were larger as a group and in an each given age, so they grew faster), maturation rates (2- or 3-year old males became mature more often) and survival (males had lower survival relative to the initial cohort size) were revealed. These sexual differences remained present despite a gradual increase in the size of mature frogs, and a decrease of their survival, corresponding to the decrease in population size.
The variance components of larval traits of two brown frog species in two widely separated populations wereestimated using full-sib/half-sib breeding design and raising the tadpoles under laboratory conditions. The means of length of larval period (LP) in two species were nearly identical in each of two localities. The counter-gradient variation was revealed in size at metamorphosis (SM), LP and growth rate (GR) in R. temporaria and in LP and GR in R. arvalis. In R. temporaria from both localities, the heritability in SM was lower than in LP. In R. arvalis, the heritability in SM was higher than in LP. In both species, the heritability in GR in northern and southern populations was similar or some higher in northern population. In R. temporaria, the stronger (than in R. arvalis) infuence of parental body length (including maternal effects) on SM, LP and GR refects the importance of these traits for ftness at postmetamorphic stages of life cycle.
The influence of dates of metamorphosis, size at metamorphosis, and number of emerged juveniles on the reproductive characteristics and female body size were studied by group-marking of postmetamorphic Rana arvalis individuals of three generations. The frogs under study emerged after metamorphosis from the breeding pond and their adults were recaptured in the same pond after 3–7 years. The maximum body size, egg size, and reproductive effort were revealed in the females born in 1991. This generation is characterized by the maximum size at metamorphosis and the minimum number of emerged juveniles. At the same time, similar variations in the mean annual values of body length, fecundity, and egg diameter were revealed in females of different generations. The differences between the generations of 1989 and 1990 are less pronounced, despite the similar size at metamorphosis and about the same initial number of juveniles. An increase in the female fecundity and egg diameter (but not in reproductive effort) with age was the general trend for each generation. Mature females originating from early juveniles were, on the average, significantly younger than late juveniles of the same generation. Most of females from the group of late small-sized animals reproduced for the first time after 4th wintering, i.e. one year later than other groups. The groups distinguished within generation differed in reproductive characteristics only slightly. In the early-large female group, a positive correlation between the size at metamorphosis and rates of growth and maturation was revealed.
The influence of dates of metamorphosis (early and late), size at metamorphosis (small-, medium- and large-sized) and number of emerged juveniles on the survivorship and other fitness characteristics of females were studied by counting and group-marking of postmetamorphic Rana arvalis individuals of three generations. The females under study emerged after metamorphosis from the breeding pond and were recaptured in the same pond after 3–7 years as adults. Within the generation born in 1989, the survivorship of the group of early juveniles till first and each successive reproduction was higher than in late ones, but within the generation of 1990 this survivorship of early juveniles was lower than in late ones. The survivorship of females of 1990 was higher in comparison not only with the generation of 1989, characterized by smaller sizes at metamorphosis, also with the generation of 1991, characterized by maximum size at metamorphosis. The total number of eggs produced by a given generation was determined by premetamorphic survivorship, and correspondingly by the number of emerged juveniles of a given generation. The net rate of reproduction (calculated on the basis of life-tables) was determined by premetamorphic survivorship to a greater extent than by size at metamorphosis and survivorship till maturity. Within each generation, the net rate of reproduction of a given group was affected rather by its survivorship till each successive breeding than by fecundity. Therefore, in the generation of 1989, the early group had higher net rate of reproduction than the late one. Within the generation of 1990, the relationship between these two groups was inverse. Large-sized (both early and late) groups of 1989 had maximal net rate of reproduction, but these differences were not revealed within the generation of 1990.
Based of the long-term studies of breeding Rana temporaria females, the components of intrapopulation variation of body size and reproductive characteristics were described, and the structure of relationship between them was estimated. The relegation of individuals to a certain generation was determined by skeletochronology. Within each generation female body length, fecundity, and egg size, but not reproductive effort and the relative clutch mass increased with aging. Both the increase and decrease of annual average values of body length, fecundity and egg size in females of different generations in the same years were revealed. Both body size and age of the frogs correlated positively and significantly with their fecundity and egg size. As shown by principal component analysis, each character (except for reproductive effort strongly influenced by fecundity) varied independently. Relationship between separate pairs of characters demonstrated the same relative independence. The weaker relationship of the relative clutch mass with age (compared to the other characters), intergeneration and annual variation is stipulated by the maximum investment of females in each reproduction, the latter characteristic correlating poorly with age and size of females.
