Individual Age Determination Research Articles

Age, Growth and Longevity of Sympatric Triturus cristatus, T. marmoratus and Their Hybrids (Amphibia, Urodela): A Skeletochronological Comparison

In the ponds of some regions of France, Triturus cristatus and Triturus marmoratus coexist and natural hybrids can be found. In the course of our study examining evolutionary strategies of newts, the method of individual age determination (skeletochronology) was applied. Cross-sections of femurs and phalanges were stained with Ehrlich hematoxylin. Hematoxylinophilic lines considered to be Lines of Arrested Growth (LAG) were observed and carefully counted. Our results on longevity, median age, sexual maturity and growth rate concur with the observations on life span of the two species in allopatric situations. The general morphology of the hybrids, age at sexual maturity and median life span were intermediate between those of the parental species. In Mayenne (western France), the ranges of two closely related species of newts, Triturus cristatus (Laurenti, 1768) and T. marmoratus (La- treille, 1800) overlap (Thorn, 1968; Rafinski and

Identification des classes d’âge dans les populations de belettes (Mustela nivalis L. 1766)

King (1980) pointed out how imperfect are age determination methods in the Weasel. She argued that these imperfections mainly result from a great interpopulation variability, a strong sexual dimorphism and the population multivoltine dynamics. Because of the difficulties to find out an appropriate individual age determination method, she proposed to develop a strategy allowing to determine the age structure of the population. According to this point of view, we tried to reinforce the consistency, pertinency and generality of Carolyn King’s strategy, using arguments provided by the study of cranium and mandibula’s morphogenesis. Traits of the chronologically well known natural history of the species were put in relation with morphological changes of its cranium and its mandibula ; in this way, we were able to allocate our animals to 4 age classes (0-3 months ; 3-6 months ; 6 months -1 year ; more than one year). A sample of 565 weasels collected sequentialy, during at least 7 months in 3 localities, was apportioned according to this method. The resulting population structure was consistent with that obtained by the use of several morphometric methods. These French data corroborate the existence of a strong sexual dimorphism in this species, and its great variability in stature on a large area. It also provides circumstantial evidence for two reproductive periods during the year. A strategy of sampling and processing of a numerous sample is proposed.

Isotopic age-determinations of rocks from the British Isles, 1955–64

Over 475 individual age-determinations of British rocks, recorded in some sixty papers, have appeared during 1955–64, the decade in which isotopic dating reached practical maturity and began to have great effect in establishing the scale of events in historical geology, including that of the Pre-Cambrian. The willing co-operation of all the British laboratories in which isotopic ages are determined has enabled abstracts of these papers to be prepared for publication; the emphasis of the abstracts lies in the geological implications. In an introductory section (by P. A. Sabine& J. Watson), the number of determinations of British rocks is plotted against apparent ages. The resulting histograms are broadly similar to those derived from world-wide sources and from other countries, showing that they record not only the incidence of laboratory determinations but fundamentally significant geological events. Major peaks of activity are indicated, the implications of which are reviewed. Periods of plutonic activity are shown in the Lewisian at 2600 to 2200m.y. (Scourian) and 1600 to 1450m.y. (Laxfordian). Metamorphic rocks, migmatites, and granites from the Caledonian Belt are spread from about 750 to 360 m.y. with a weak maximum at 750 to 650 m.y. and a stronger one at 450 to 360 m.y. In south-west England metamorphic activity yields dates from 400 to 350m.y., and Hercynian granites dates from 300 to 250 m.y. Tertiary granites and allied rocks are mainly 65 to 50 m.y. old. In each abstract an attempt is made to include geographical locality, character and geological relationships of specimens investigated, method employed, and constants used, ages obtained, and conclusions drawn. Full indexes are provided.