Digit length ratio (2D/4D): comparing measurements from X-rays and photographs in field voles ( Microtus agrestis ) (original) (raw)
Related papers
Frontiers in endocrinology, 2014
Digit ratio (2D:4D) denotes the relative length of the second and fourth digits. This ratio is considered to be a biomarker of the balance between fetal testosterone (T) and estrogen (E) in a narrow window of early ontogeny. Evidence for this assertion is derived from direct and indirect measures of prenatal hormonal exposure (in experimental animals, via amniotic fluid samples and in the study of sex-typical traits) in relation to 2D:4D. In contrast, the relationships between 2D:4D and levels of sex steroids in adults are less clear, as many correlational studies of 2D:4D and adult sex steroids have concluded that this association is statistically non-significant. Here, we suggest that in order to understand the link between 2D:4D and sex hormones, one must consider both fetal organizing and adult activating effects of T and E. In particular, we hypothesize that 2D:4D correlates with organizing effects on the endocrine system that moderate activating effects in adulthood. We argue ...
Digit ratio (2D:4D) denotes the relative length of the second and fourth digits. This ratio is considered to be a biomarker of the balance between fetal testosterone (T) and estrogen (E) in a narrow window of early ontogeny. Evidence for this assertion is derived from direct and indirect measures of prenatal hormonal exposure (in experimental animals, via amni-otic fluid samples and in the study of sex-typical traits) in relation to 2D:4D. In contrast, the relationships between 2D:4D and levels of sex steroids in adults are less clear, as many correlational studies of 2D:4D and adult sex steroids have concluded that this association is statistically non-significant. Here, we suggest that in order to understand the link between 2D:4D and sex hormones, one must consider both fetal organizing and adult activating effects of T and E. In particular, we hypothesize that 2D:4D correlates with organizing effects on the endocrine system that moderate activating effects in adulthood. We argue that this is particularly evident in " challenging " conditions such as aggressive and sexual encounters, in which individuals show increased levels of T. We discuss this refinement of the 2D:4D paradigm in relation to the links between 2D:4D and sports performance, and aggression.
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2016
Sexual dimorphism in the ratio of digit lengths has been correlated to behavioral, physiological, and morphological traits in a variety of taxa. While sexual dimorphism in the second-to-fourth digit length ratio (2D:4D) is a well-established indicator of prenatal androgen exposure in mammals, investigations into the patterns of 2D:4D and the drivers of such variation in other taxa are lacking. We used linear mixed effects models to gain a mechanistic understanding of the factors that drive variation in the scaling relationship between the lengths of the second and fourth digits in two species of anurans: t ungara frogs (Engystomops pustulosus) and cane toads (Rhinella marina). We found evidence for sexual dimorphism of the 2D:4D scaling relationship on the front feet of t ungara frogs, with female frogs having a larger ratio than males resulting from a relatively longer second digit on females. To our knowledge, this mammal-like pattern of sex differences in digit ratio has not yet been reported for anurans. However, given the reduced number of digits on the front feet of anurans, and uncertainty about which digit was lost during evolutionary history, this apparent sexual dimorphism in the front feet of t ungara frogs should be treated with caution. In contrast, we found no evidence of sexual dimorphism in 2D:4D on either the front or rear feet of cane toads. This study highlights ambiguities in 2D:4D across taxa and suggests that further research is needed to evaluate the effect of androgens on 2D:4D in animals other than placental mammals.
Sexual dimorphism in brain weight of meadow voles: role of gonadal hormones
Developmental Brain Research, 1990
In most adult mammals, brain weights of males exceed those of females. The role of androgens in the genesis of this sex difference was assessed in meadow voles by acute neonatal or chronic postweaning manipulation of testosterone titers. Female voles given a single injection of testosterone propionate (TP) on the second day of postnatal life had brain weights in adulthood that were indistinguishable from those of male voles and significantly heavier than those of control females. Whole brain DNA content, a measure of cell number, was not increased by neonatal TP treatment. Females treated with TP from day 19 to 70 had lower brain weights than control females and males gonadectomized at 19 days of age had greater brain weights than did intact male voles at day 70. The sex dimorphism in brain weight reflects organizational effects of testosterone during perinatal development. Beginning at weaning, and continuing through postpubertal development, testosterone decreases brain weight in both sexes. We suggest that testosterone affects brain weight by altering cell size or non-cellular components rather than cell number.
Background: Developmental associations often explain phenotypic integration. The intersected hormonal regulation of ontogenetic processes fosters predictions of steroid-mediated phenotypic integration among sexually dimorphic traits, a statement defied by associations between classical dimorphism predictors (e.g. body size) and traits that apparently lack sex-specific functions (e.g. ratios between the lengths of Digits II and IV-2D:4D). Developmental bases of female-biased 2D:4D have been identified, but these remain unclear for taxa presenting male-biased 2D:4D (e.g. anura). Here we propose two alternative hypotheses to investigate evolution of male-biased 2D:4D associated with sexually dimorphic body size using Leptodactylus frogs: I)'hypothesis of sex-specific digit responses'-Digit IV would be reactive to testosterone but exhibit responses in the opposite direction of those observed in female-biased 2D:4D lineages, so that Digit IV turns shorter in males; II) 'hypothesis of identity of the dimorphic digit'-Digit II would be the dimorphic digit. Results: We compiled the following databases using Leptodactylus frogs: 1) adults of two species from natural populations and 2) testosterone-treated L. fuscus at post-metamorphic stage. Studied traits seem monomorphic in L. fuscus; L. podicipinus exhibits male-biased 2D:4D. When present, 2D:4D dimorphism was male-biased and associated with dimorphic body size; sex differences resided on Digit II instead of IV, corroborating our 'hypothesis of identity of the dimorphic digit'. Developmental steroid roles were validated: testosterone-treated L. fuscus frogs were smaller and exhibited masculinized 2D:4D, and Digit II was the digit that responded to testosterone. Conclusion: We propose a model where evolution of sexual dimorphism in 2D:4D first originates from the advent, in a given digit, of increased tissue sensitivity to steroids. Phenotypic integration with other sexually dimorphic traits would then occur through multi-trait hormonal effects during development. Such process of phenotypic integration seems fitness-independent in its origin and might explain several cases of steroid-mediated integration among sexually dimorphic traits.
Human Biology Review, 2023
The second-to-fourth digit (2D:4D) ratio is a sexually dimorphic trait, with men having lower ratios than women, indicating relatively higher prenatal testosterone exposure compared to oestrogen. The 2D:4D ratio is fixed in intrauterine conditions that are affected by foetal sex steroids (testosterone and oestrogen) and an indirect method to determine intrauterine sex hormone levels that significantly correlate with somatic features, behavioural traits, fertility measures, reproductive characteristics, and predisposition to certain chronic diseases. Researchers discovered that a more masculine (low 2D<4D) digit ratio and a more feminine (high; 2D>4D) digit ratio are manifestations of increased prenatal testosterone and oestrogen exposure, respectively. Furthermore, digit ratio (2D:4D) values are widely used to predict reproductive capacity and success, fertility measures, natural menopause, and age at menarche, which varies between populations. The current review paper attempted to discuss sexual dimorphism in 2D:4D ratios, as well as its potential association and utility in evaluating certain reproductive characteristics and behavioural traits in populations. Methodological comparisons, benefits and drawbacks of determining the 2D:4D for studying the effect of prenatal sex steroids are also highlighted.
RESUMEN Estudiamos los ciclos de esteroides sexuales de machos y hembras en estado silvestre de la tortuga del Bolsón en la Reserva de la Biósfera de Mapimí (Durango). Tomamos muestras de sangre por venipunción de la yugular a intervalos bisemanales durante un período de 14 meses, determinándose los niveles circulantes de esteroides por medio de radioinmunoensayos. Los niveles hormonales mostraron tendencias estacionales. En las hembras, la testosterona tuvo un valor máximo al salir de la brumación, en asociación con el incremento en la receptividad sexual, y el nivel de estradiol aumentó después de la emergencia asociado con la maduración folicular. El nivel de estos dos esteroides se incrementó con las lluvias estacionales, cuando ocurrieron el crecimiento folicular y la vitelogénesis. La progesterona mostró niveles bajos a la emergencia, los cuales aumentaron con el incremento de la duración del dia y la temperatura, llegando al máximo antes del pico de la oviposición. La caída en los niveles de las tres hormonas estuvo asociada con la oviposición. Las hembras probablemente almacenan esperma durante parte del otoño y el invierno para usarlo en la siguiente estación reproductiva. Los machos salieron de la hibernación con bajos niveles de testosterona, pero exhibieron conductas reproductivas poco después. Junto con un incremento de la testosterona, el cortejo y la frecuencia de apareamientos se incrementaron con estímulos ambientales, prolongándose hasta principios del otoño. Los niveles de testosterona y la actividad reproductiva disminuyeron conforme se aproximaba el inicio de la hibernación. Los niveles máximos de testosterona en machos de esta especie son mayores que los conocidos para cualquier otro vertebrado. ABSTRACT This study describes sex-steroid cycles of free-living male and female Bolson tortoises at the Mapimi Biosphere Reserve in northeastern Durango, Mexico. Blood samples were taken at biweekly intervals during a 14 month period by jugular venipuncture, and plasma levels of steroids were determined using radioimmunoassays. Hormone levels showed seasonal trends. In females testosterone peaked following emergence, associated with increased sexual receptivity, and estradiol increased after emergence in association with follicular maturation. These two steroids increased with seasonal rains, when follicular enlargement and vitellogenesis occurred. Females emerged from brumation with low levels of progesterone,
Brain Research, 1986
The organization of neuronal cell bodies in the caudal preoptic area (POA) and rostral anterior hypothalamic area (AH) was studied in Nissl-stained brain sections from adult male and female ferrets. Computer-assisted image-analysis procedures were developed to help estimate the areas of cellular density and the sizes of individual perikarya. At the junction of the POA and AH, a bilateral dorsal-medial group of neurons was apparent only in male ferrets (dorsal nucleus). At the same coronal level, a ventral-medial group of neurons was apparent bilaterally in both males and females (ventral nucleus). The mean somal area of cells in the dorsal nucleus of males was significantly greater than the mean somal area of cells in the corresponding dorsal region of females or in the ventral nucleus of both sexes. The dorsal nucleus was clearly discernible in adult males regardless of their hormonal status, although cells in the dorsal nucleus were larger in intact breeding males or gonadectomized males given testosterone, estradiol or dihydrotestosterone than in gonadectomized males given no gonadal hormones or given progesterone. Neither the grouping of large cells nor the steroid-induced increase in cell size, characteristic of the male dorsal nucleus, was seen in the comparable dorsal region of females. The sex difference in cellular organization observed in the ferret at the junction of the POA and AH is the first difference of this type to be seen in the POA/AH of a non-rodent mammalian species. Its identification will, hopefully, aid in the analysis of the neural mechanisms that control various sex-specific behaviors in this species.