The central-marginal model is widely accepted in chromosomally polymorphic species of Drosophila. In fact, geographically and ecologically central populations of Drosophila show higher levels of polymorphism for paracentric inversions, whereas marginal populations tend to be monomorphic. This fact has been variously explained. Chromosomal polymorphisms in grasshoppers have also been attributed to show such geographical structuring, as in the case of the South-American grasshopper Dichroplus pratensis Bruner (Orthoptera: Acrididae). However, in three other cases involving Acrididae – Leptysma argentina Bruner, Trimerotropis pallidipennis (Burmeister) and Cornops aquaticum (Bruner), it is clear that chromosomal polymorphisms (sometimes with a wide extension over the Argentine area) do not conform to this pattern, and show instead clear correlations with environmental variables, especially minimum temperature, showing low or null frequencies of the rearrangements at one extreme of the environmental gradient and with high or fixed frequencies at the other. Furthermore, this correlation with temperature might also be true in the case of D. pratensis. These aforementioned examples emphasise the dangers of over-generalization when discussing chromosomal polymorphisms, and suggests that such polymorphisms should be considered very much in a case-specific manner in terms of the particular genetic system under study., Pablo C. Colombo., and Obsahuje seznam literatury
Amongst the non-native Ponto-Caspian gobies that have invaded the Middle Danube is the monkey goby Neogobius fluviatilis (Pallas, 1814). Despite a strong specialization towards sandy substratum, revealed in a previous study, monkey goby is considered an invasive species and therefore should demonstrate great plasticity in its biological traits. The main aim of the present study was to evaluate the age and growth of a non-native population of monkey goby from the River Ipeľ in Slovakia. Six age groups (0 – V) were observed in the sample from the River Ipeľ (n = 165), with males demonstrating faster growth than females, which was reflected both in the smoothing cubic B-spline model and in the annual increment. The cubic B-spline model indicated a reverse Lee’s phenomenon, especially in males, which is likely to have arisen from the size selective mortality. Growth of invading monkey goby from the River Ipeľ was slower than that reported for the species’ native range. Together with other growth patterns, this may suggest (among other possible explanations) a greater allocation of resources to reproduction than to somatic growth, which is a life-history pattern typical for newly established populations of successful invaders.
Growth patterns of the golden loach, Sabanejewia balcanica were examined in the Rijeka River in Central Croatia on a total of 77 specimens collected in a single sampling session in June 2006. No significant difference was found in total body length between males and females. Age was determined from otoliths. Both males and females live 4 years, though due to the sampling period, no 0+ age fish were found in this study. The length-weight relationship was calculated as W=2x10-6TL3.3229 for males and W=3x10-6TL3.2811 for females, indicating positively allometric growth. According to the growth factor k, growth of males was three times faster than that of females.
A total of 174 specimens of the spined loach Cobitis taenia Linnaeus, 1758, comprising 117 females, 45 males and 12 juveniles, from Lake Klawoj (Poland) were identified as C. taenia from their karyotype (2n = 48 chromosomes). The overall sex ratio (M:F = 1:2.6) showed that females dominated in the population, but this varied with increasing fish size. Age and growth were determined based on otolith measurements. Standard lengths were back- calculated from the regression of fish standard length on the otolith radius and the growth pattern was described using the von Bertalanffy model separately for males and females, which revealed a strong fit for both females (Lt =92.4(1– exp(–0.278 (t – 0.456)); r2 = 0.803) and males (Lt=120.6(1 – exp(– 0.227 (t – 0.558); r2= 0.772). Comparison of asymptotic length with maximum observed size of males and females revealed that all values were a bit overestimated (as per the Taylor criteria). The SL – weight equations for males (W = 0.0003 SL3.8377; r2 = 0.8961) and females (W = 0.0039 SL3.1683; r2 = 0.9616) indicated allometric growth in both sexes, though more so in males than in females.