Maternal corticosterone but not testosterone level is associated with the ratio of second-to-fourth digit length (2D:4D) in field vole offspring (Microtus agrestis) Thomas Lilley a, ⁎, Toni Laaksonen a , Otso Huitu b , Samuli Helle a a Section of Ecology, Department of Biology, University of Turku, FI-20014, Turku, Finland b Finnish Forest Research Institute, Suonenjoki Research Unit, Juntintie 154, FI-77600 Suonenjoki, Finland abstract article info Article history: Received 22 June 2009 Received in revised form 7 September 2009 Accepted 23 November 2009 Available online xxxx Keywords: Phenotypic marker Intrauterine Steroids Early development Maternal effect The steroid environment encountered by a foetus can strongly affect its post-natal physiology and behaviour. It has been proposed that steroid concentrations experienced in utero could be estimated from adults by measuring their second-to-fourth digit length ratio (2D:4D). However, there is still little direct evidence that intra-uterine steroid levels affect individual 2D:4D. We examined whether maternal pre-pregnancy testosterone and corticosterone levels (as estimates of intra-uterine testosterone and corticosterone exposure) affected the 2D:4D of pups in non-domesticated field voles (Microtus agrestis), measured by X-rays at the age of weaning (21 days). Furthermore, for the first time in a non-human species, we studied whether testosterone and corticosterone levels correlated with 2D:4D in adult females. We found that the maternal pre-pregnancy level of testosterone was not associated with offspring 2D:4D in either the left or the right paw. Instead, maternal pre-pregnancy corticosterone level was positively correlated with offspring 2D:4D in the right paw, but unrelated to 2D:4D in the left paw. In addition, the 2D:4D of adult females was not associated with either their circulating testosterone or corticosterone levels. Our results suggest that in field voles maternally administered testosterone is not a major determinant of offspring 2D:4D, whereas maternal stress appears to account for some of the variation in the 2D:4D of their offspring. © 2009 Elsevier Inc. All rights reserved. 1. Introduction The ratio of second-to-fourth digit length (hereafter 2D:4D) has been highlighted as a useful adult-age marker of prenatal exposure to steroids [25,26,31] that are likely to have strong effects on vertebrate physiology, behaviour and reproduction [33]. In many species, the steroid environment encountered by developing foetuses is very difficult to measure accurately, due to ethical and practical reasons [32]. Therefore, the notion that 2D:4D is a reliable marker of prenatal exposure to steroids rests mainly on indirect evidence, for example regarding sex differences in adult 2D:4D (humans; [26,44], birds; [4,37,41,45], non- human mammals; [5,21,27], reptiles; [8,42]), and the temporal stability of 2D:4D with age [30,47]. However, not all studies have managed to establish a sex difference in 2D:4D [2,11,24] or found that 2D:4D remains unaltered from birth [1,5,6,22,28,29]. Currently the strongest evidence for a link between prenatal steroid concentrations and 2D:4D is provided by recent experimental studies in mammals [46] and birds [45]. For example, Talarovičová et al. [46] found that experimentally elevated levels of maternal testosterone in rats resulted in decreased 2D:4D ratios of offspring. However, these results were based on a rather small sample size, as only three pregnant females were manipulated with testosterone and the subsequent digit ratio measures were based on only eight pups born. More studies, especially on mammals, are therefore highly called for. Although there is evidence for a leakage of testosterone from male foetuses to neighbouring foetuses (i.e., effects of intra-uterine positioning (IUP), [43]), it is likely that steroid levels in maternal circulation approximately reflect those experienced by the developing embryos, as testosterone levels should be rather stable across maternal tissues [32]. This assumption is supported by reports that have found that systematic administration of testosterone to pregnant female rats in laboratory conditions results in behavioural masculin- ization of female offspring [17]. Systematic administration of testosterone to pregnant sheep has also been found to result in behavioural and physical masculinization in lambs [39]. Pregnant rats have also shown considerable differences in blood androgen levels, which may, in part, be a possible source of the variation in masculinization of offspring between litters [12]. Transfer of andro- gens from maternal blood to foetal circulation was provided as an explanation for these findings. It could thus be predicted that maternal testosterone level might also influence the 2D:4D of pups [9]. However, to our knowledge, an association between maternal serum testosterone and offspring 2D:4D has not yet been studied. In addition to maternal steroids, maternal stress also affects the development of the embryos [16,50]. For example, high levels of Physiology & Behavior xxx (2010) xxx–xxx ⁎ Corresponding author. Tel.: +358 2 333 6084; fax: +358 2 333 6550. E-mail address: tmlill@utu.fi (T. Lilley). PHB-08982; No of Pages 5 0031-9384/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2009.11.015 Contents lists available at ScienceDirect Physiology & Behavior journal homepage: www.elsevier.com/locate/phb ARTICLE IN PRESS Please cite this article as: Lilley T, et al, Maternal corticosterone but not testosterone level is associated with the ratio of second-to-fourth digit length (2D:4D) in field vole offspring (Microtus agrestis), Physiol Behav (2010), doi:10.1016/j.physbeh.2009.11.015