Age, Growth and Other Population Characteristics of Bufo bufo from Different Latitudes and Altitudes

Abstract

Five populations of common toads from different latitudes and altitudes in Europe were studied, mainly by skeletochronological annalysis of their phalanges. The toads from the populations from Germany, The Netherlands, Norway and Switzerland definitely concerned Bufo bufo bufo, those from the population from France might have concerned Bufo bufo spinosus. At metamorphosis, both sexes grow at the same rate in each population. Sexual dimorphism concerning growth becomes apparent at about the minimum age of maturation of male toads or one year before. Male toads can reach maturity at least one year before females can. Maturity can be reached when the growth rate is reduced to 21% of the growth rate at metamorphosis in males, and to 21%-28% of that in females, the latter dependent on the length of the sexual cycle. The proportion of sexually mature toads in each age class was estimated. The age at which 95% of the toads were estimated to be sexually mature corresponds with the average age at which the toads have reached 95% of their maximal size, except for toads with a biennial sexual cycle. The latter continue growth for longer. Toads from northern latitude (Norway) and high altitude (Switzerland) grow slower, may reach older ages and larger maximal sizes than those from southern latitude and low altitude (Germany and The Netherlands). The former toads also mature at older ages and at larger sizes than the latter. However, when growth is corrected for interpopulational differences in the seasonal activity of the toads, the former toads actually grow faster and the differences concerning the time at which maturity is reached no longer exist among the toads of the four populations mentioned. Male and female toads from these populations can reach maturity after having spent 1.09 (ranging from 1.07 to 1.15) and 1.55 (ranging from 1.50 to 1.59) years on growth respectively. In addition, the sexually dimorphic growth coefficient, which describes how growth proceeds, is also equal among those toads, ranging from 1.44 to 1.56 for males (average 1.48) and from 0.84 to 0.98 for females (average 0.92). The toads from France were exceptional in many ways. Among others, they grow much faster than the other toads, they can reach larger maximal sizes and mature only after having spent 1.77 (males) and 2.49 (females) years on growth. The growth coefficient found in these toads was also different, amounting to 0.80 for males and 0.54 for females. The geographical distribution of the common toad Bufo bufo bufo (L.) extends from North-West Africa over entire Europe (except for the extreme North, Ireland and the Mediterranean isles) to Japan (Angel, 1946; Mertens, 1947). However, in the South of Europe other varieties occur, in- cluding Bufo bufo spinosus Daudin which is most conspicuous by its large body size and the thorny warts on its back (Mertens, 1947). Although common toads usually oc- cur at low altitudes, they can be found up to an altitude of 2200 m in the Alps (Angel, 1946). Because of their extended distribution