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The present study was based on the bacula of 39 male (17 juvenile, 22 adult) stone marten (Martes foina) samples obtained from all geographical regions of Turkey between 1995 and 2016. Morphological variability in 11 characteristics of bacula was investigated. The purpose of this study was to measure numerical characters of the baculum, to identify relationships between measurements, and to evaluate variabilities in its morphology. Weight, total length, base length, base height, base width, apex height, apex width, median width, and median height were significantly greater in the bacula of adults compared to the bacula of juveniles. The most variable characteristic in adults was base width (18.96%). There was a significant relationship between some characteristics of the bacula measured. The strongest positive relationships were observed between median height and baculum weight (r = 0.771), weight and base length (r = 0.755), and median width and weight (r = 0.750) characteristics. Statistical analysis (PCA) also revealed a strong relationship between some characteristics. In particular, positive correlations between width and height sizes in the base (proximal), median, and distal of the baculum, as well as axis-apex height and apex width, suggest relationships that protect the urethra and baculum from fissures and fractures during copulation. [ABSTRACT FROM AUTHOR]

The baculum (os penis) is a mineralized bone within the glans of the mammalian penis and is one of the most morphologically diverse structures in the mammal skeleton. Recent experimental work provides compelling evidence for sexual selection shaping the baculum, yet the functional mechanism by which this occurs remains unknown. Previous studies have tested biomechanical hypotheses for the role of the baculum based on simple metrics such as length and diameter, ignoring the wealth of additional shape complexity present. For the first time, to our knowledge, we apply a computational simulation approach (finite-element analysis; FEA) to quantify the three-dimensional biomechanical performance of carnivoran bacula (n = 74) based upon high-resolution micro-computed tomography scans. We find a marginally significant positive correlation between sexual size dimorphism and baculum stress under compressive loading, counter to the 'vaginal friction' hypothesis of bacula becoming more robust to overcome resistance during initial intromission. However, a highly significant negative relationship exists between intromission duration and baculum stress under dorsoventral bending. Furthermore, additional FEA simulations confirm that the presence of a ventral groove would reduce deformation of the urethra. We take this as evidence in support of the 'prolonged intromission' hypothesis, suggesting the carnivoran baculum has evolved in response to pressures on the duration of copulation and protection of the urethra. [ABSTRACT FROM AUTHOR]

In this study we investigated allometry and variation in the baculum of the stoat Mustela erminea and compared it with head-and-body length not involved in reproduction. The stoat is a species with pre-copulatory selection (manifested by the high degree of malebiased sexual size dimorphism) therefore we predicted that baculum allometry may be isometric or exhibited negative allometry. We also test the hypothesis that the baculum size is positively correlated with adult body size and may be used as a reliable indicator of male good condition. Results presented in this study were different according to which regression model type was used. While the OLS slope for baculum length in M. erminea indicated negative allometry, the RMA model showed positive allometry. The results obtained for M. erminea weren't in agreement with mentioned hypothesis that if baculum allometry is affected by the degree of pre-copulatory selection relative to post-copulatory selection, then we predict isometry or negative allometry of the baculum. Nevertheless, we suggest, that to confirm the above statements further analysis of more numerous material of M. erminea coupled with comparative analysis of testicular growth studies are needed to fully understand the importance and function of the baculum relative to the mating system. [ABSTRACT FROM AUTHOR]

Copyright of Therya is the property of Asociacion Mexicana de Mastozoologia, A. C. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The extreme morphological variability of the baculum across mammals is thought to be the result of sexual selection (particularly, high levels of postcopulatory selection). However, the evolutionary trajectory of the mammalian baculumis little studied and evidence for the adaptive function of the baculum has so far been elusive. Here, we use Markov chain Monte Carlo methods implemented in a Bayesian phylogenetic framework to reconstruct baculum evolution across the mammalian class and investigate the rate of baculum length evolution within the primate order. We then test the effects of testes mass (postcopulatory sexual selection), polygamy, seasonal breeding and intromission duration on the baculum in primates and carnivores. The ancestral mammal did not have a baculum, but both ancestral primates and carnivores did. No relationship was found between testes mass and baculum length in either primates or carnivores. Intromission duration correlated with baculum presence over the course of primate evolution, and prolonged intromission predicts significantly longer bacula in extant primates and carnivores. Both polygamous and seasonal breeding systems predict significantly longer bacula in primates. These results suggest the baculum plays an important role in facilitating reproductive strategies in populations with high levels of postcopulatory sexual selection. [ABSTRACT FROM AUTHOR]

Mammalian penises are morphologically diverse, including a highly variable and taxonomically informative baculum (os penis), and variable penile spines, both of which are possessed by many--but not all--species. To understand the evolution of genital morphologies, as well as the potential role of both the baculum, and penile spines that directly interact with female reproductive tract, we undertook a comparative study of male penile spines and their relationship with the baculum across all mammalian orders. Specifically, we investigated several factors that may explain the presence or absence of penile spines in mammals, including mating system, risk of sperm competition, female reproductive physiology, presence and width of the baculum, and phylogenetic history. We observed that the presence of both the baculum and penile spines is correlated with residual testes size, suggesting a potential role in sexual selection for these traits. We found no association between the presence of spines and mating system, or with the presence/width of the baculum, although relative testes mass was marginally associated with baculum width. We found no relationship between baculum presence or width and mating system. We also noted that spines presence or absence have an orderlevel distribution, and clear phylogenetic patterns of distribution across mammals. It is likely that spine morphology and distribution, not just presence, play an important role in genital evolution in mammals, but these features are poorly described in most groups. Quantitative data collection in most mammalian taxa would be useful to further elucidate the evolution of the complex genital morphology of this group. [ABSTRACT FROM AUTHOR]

The rapid evolution of male genitalia is a nearly ubiquitous pattern across sexually reproducing organisms, likely driven by the evolutionary pressures of male-male competition, male-female interactions, and perhaps pleiotropic effects of selection. The penis of many mammalian species contains a baculum, a bone that displays astonishing morphological diversity. The evolution of baculum size and shape does not consistently correlate with any aspects of mating system, hindering our understanding of the evolutionary processes affecting it. One potential explanation for the lack of consistent comparative results is that the baculum is not actually a homologous structure. If the baculum of different groups evolved independently, then the assumption of homology inherent in comparative studies is violated. Here, we specifically test this hypothesis by modeling the presence/absence of bacula of 954 mammalian species across a wellestablished phylogeny and show that the baculum evolved a minimum of nine times, and was lost a minimum of ten times. Three different forms of bootstrapping show our results are robust to species sampling. Furthermore, groups with a baculum show evidence of higher rates of diversification. Our study offers an explanation for the inconsistent results in the literature, and provides insight into the evolution of this remarkable structure. [ABSTRACT FROM AUTHOR]

The rapid divergence of male genitalia is a preeminent evolutionary pattern. This rapid divergence is especially striking in the baculum, a bone that occurs in the penis of many mammalian species. Closely related species often display diverse baculum morphology where no other morphological differences can be discerned. While this fundamental pattern of evolution has been appreciated at the level of gross morphology, nearly nothing is known about the genetic basis of size and shape divergence. Quantifying the genetic basis of baculum size and shape variation has been difficult because these structures generally lack obvious landmarks, so comparing them in three dimensions is not straightforward. Here, we develop a novel morphometric approach to quantify size and shape variation from three-dimensional micro-CT scans taken from 369 bacula, representing 75 distinct strains of the BXD family of mice. We identify two quantitative trait loci (QTL) that explain ~50% of the variance in baculum size, and a third QTL that explains more than 20% of the variance in shape. Together, our study demonstrates that baculum morphology may diverge relatively easily, with mutations at a few loci of large effect that independently modulate size and shape. Based on a combination of bioinformatic investigations and new data on RNA expression, we prioritized these QTL to 16 candidate genes, which have hypothesized roles in bone morphogenesis and may enable future genetic manipulation of baculum morphology. [ABSTRACT FROM AUTHOR]

In this study we investigated variation in the baculum of the stone marten, Martes foina from the Czech part of Silesia (north-eastern Czech Republic). The aim of this study was to assess quantitative characteristics of the baculum size, relationships between measurements and description of the variability in baculum morphology. The study presents the morphological variation in six dimensional traits of the baculum based on an analysis of 15 specimens collected in the vicinity of Opava and deposited at the Šariš Museum Bardejov (Slovakia). The descriptive statistics revealed size variation of the bacula, while the statictic analysis (PCA) showed a strong positive correlation between morphological traits of the body and baculum. [ABSTRACT FROM AUTHOR]

The baculum (os penis) has been extensively studied as a taxon-specific character in bats and other mammals but its mechanical function is still unclear. There is a wide consensus in the literature that the baculum is probably a sexually selected character. Using a novel approach combining postmortem manipulation and three-dimensional (3D) imaging, we tested two functional hypotheses in the common noctule bat Nyctalus noctula, the common pipistrelle Pipistrellus pipistrellus, and Nathusius' pipistrelle Pipistrellus nathusii: (i) whether the baculum can protect the distal urethra and urethral opening from compression during erection and copulation; and (ii) whether the baculum and corpora cavernosa form a functional unit to support both the penile shaft and the more distal glans tip. In freshly dead or frozen and thawed bats, we compared flaccid penises with artificially 'erect' penises that were inflated with 10% formalin. Penises were stained with alcoholic iodine and imaged with a lab-based high-resolution x-ray microtomography system. Analysis of the 3D images enabled us to compare the changes in relative positions of the baculum, corpora cavernosa, urethra, and corpus spongiosum with one another between flaccid and 'erect' penises. Our results support both functional hypotheses, indicating that the baculum probably performs two different roles during erection. Our approach should prove valuable for comparing and testing the functions of different baculum morphologies in bats and other mammals. Moreover, we have validated an essential component of the groundwork necessary to extend this approach with finite element analysis for quantitative 3D biomechanical modeling of penis function. [ABSTRACT FROM AUTHOR]

The morphological variability of the baculum (os penis) of 147 adult specimens of species in the genus Nannospalax from 58 localities in Turkey was examined using morphological and numerical taxonomic methods. Significant differences among all of the Turkish species in the genus were determined by morphological and biometrical comparison of the bacula, and the results of this study showed that N. nehringi and N. xanthodon are separate species and that the names are not synonyms. Additionally, because the central Anatolian mole rat populations that were classified by previous studies as members of N. nehringi or N. xanthodon had highly different baculum morphologies, these populations were classified as a different species (N. labaumei) in this study. When compared to the other populations, the central Anatolian populations, which have greater diploid chromosomal sets (2n = 56, 58, 60), had very different baculum morphologies. Whereas individuals of the species N. labaumei had the smallest bacula, the largest baculum occurred in a representative of the species N. leucodon. From this study, the results indicate that 5 different blind mole rat species (N. ehrenbergi, N. leucodon, N. nehringi, N. xanthodon, and N. labaumei) live in Turkey, and in addition to these species, some of the chromosomal races (2n = 36, 40, 52) should be treated as distinct species. [ABSTRACT FROM AUTHOR]

Male genitalia exhibit a taxonomically widespread pattern of rapid and divergent evolution. Sexual selection is generally believed to be responsible for these patterns of evolutionary divergence, although empirical support for the sexual selection hypothesis comes mainly from studies of insects. Here we show that sexual selection is responsible for an evolutionary divergence in baculum morphology among populations of house mice Mus domesticus. We sourced mice from three isolated populations known to be subject to differing strengths of postcopulatory sexual selection and bred them under common-garden conditions. Mice from populations with strong postcopulatory sexual selection had bacula that were relatively thicker compared with mice from populations with weak selection. We used experimental evolution to determine whether these patterns of divergence could be ascribed to postcopulatory sexual selection. After 27 generations of experimental evolution, populations of mice subjected to postcopulatory sexual selection evolved bacula that were relatively thicker than populations subjected to enforced monogamy. Our data thereby provide evidence that postcopulatory sexual selection underlies an evolutionary divergence in the mammalian baculum and supports the hypothesis that sexual selection plays a general role in the evolution of male genital morphology across evolutionary diverse taxonomic groups. [ABSTRACT FROM AUTHOR]

The fossil bacula, or os penis, constitutes a rare subject of study due to its scarcity in the fossil record. In the present paper we describe five bacula attributed to the bear Indarctos arctoides Depéret, 1895 from the Batallones-3 site (Madrid Basin, Spain). Both the length and morphology of this fossil bacula enabled us to make interpretative approaches to a series of ecological and ethological characters of this bear. Thus, we suggest that I. arctoides could have had prolonged periods of intromission and/or maintenance of intromission during the post-ejaculatory intervals, a multi-male mating system and large home range sizes and/or lower population density. Its size might also have helped females to choose from among the available males. [ABSTRACT FROM AUTHOR]

Background: Diversity in penile morphology is characterised by extraordinary variation in the size and shape of the baculum (penis bone) found in many mammals. Although functionally enigmatic, diversity in baculum form is hypothesised to result from sexual selection. According to this hypothesis, the baculum should influence the outcome of reproductive competition among males within promiscuous mating systems. However, a test of this key prediction is currently lacking. Results: Here we show that baculum size explains significant variation in the reproductive success of male house mice under competitive conditions. After controlling for body size and other reproductive traits, the width (but not length) of the house mouse baculum predicts both the mean number of offspring sired per litter and total number of offspring sired. Conclusions: By providing the first evidence linking baculum morphology to male reproductive success, our results support the hypothesis that evolutionary diversity in baculum form is driven by sexual selection. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article discusses a study aimed at analyzing relationships between baculum size and body measurements and investigates whether the size of the baculum was correlated with body condition. The polecat bones used in the study came from the collection of the Department of Natural History, Sarisské Museum, Bardejob in Slovakia. It refers to Mustelidae as a group where a multi-male mating system happens in many species and which is one of the drivers of sperm competition. It indicates that holders of exaggerated features are preferred by females as breeding partners and the risk of losses like fracture of the baculum is outweighed by the benefits of increased reproduction caused by a greater attractiveness to the opposite sex.

We determined ringed seal (Pusa hispida) bacular and testicular growth relationships and made interspecific comparisons to species with better-known mating systems to elaborate on current hypotheses about the mating system of the ringed seal. We measured 161 bacula, 251 pairs of testes, and 55 mandibles collected from ringed seals of known age from Inuit subsistence harvests in Arviat and Sanikiluaq, Nunavut, Canada, from 2003 to 2006. Ringed seal bacular and testicular sizes were positively allometric relative to mandibular size for immature males (>7 years of age) but increased isometrically in mature males (≥ years of age), similar to relationships between bacular size and body length for known polygynous pinnipeds. Adult isometric growth contrasted with harp seals (Pagophilus groenlandicus), a promiscuous species, in which bacular size likely is sexually selected. Our results, combined with previously reported ecological and behavioral ringed seal characteristics, suggest that ringed seals display a polygynous mating system. [ABSTRACT FROM AUTHOR]

In 2000, 2002, and 2006 we captured small mammals in the Liangshan Mountains, Mabian Dafengding National Nature Reserve and Meigu Dafengding National Nature Reserve, Sichuan Province, China. Among the collected specimens we identified a new species of the genus Proedromys. Its identifying characteristics are its relatively long tail, broad upper incisors without grooves, comparatively short lower incisors, and features of the molar teeth. The glans penis of the new species also is distinctive, the proximal and distal bacula are bony, whereas the lateral bacula are only slightly ossified. The proximal baculum is flask-shaped, the distal baculum is cap-shaped, and the lateral bacula are stick-shaped. This species is associated with high-elevation spruce-fir forest habitat, an unusual setting for Proedromys across its geographic range. [ABSTRACT FROM AUTHOR]

Animals adapted to high latitude environments typically live at relatively low densities and require large areas to acquire the requisites for successful reproduction. Also, the unpredictable distribution of energy across time and space, such as environmental seasonality, constrains the timing of mating and parturition and imposes limitations to reproductive strategies. For example, limited mobility due to snow accumulation may reduce mate encounters, and this selective pressure may have resulted in morphological adaptations to assess mate quality during serial encounters. We tested whether mammalian carnivores living in high latitude environments displayed greater use of copulatory competition via length of the penis bone or baculum, and whether females in such settings enhance competition among males via multi-male matings. We then examined how baculum length may correlate with other reproductive adaptations in high latitude environments such as delayed implantation and induced ovulation. Statistical methods that account for phylogeny revealed that longer bacula occur in carnivores living in high latitude environments with greater snow accumulation, and that larger bacula is also associated with delayed implantation and multi-male mating systems. In contrast, the smallest bacula were observed in polygynous species. Our results provide an example of the effects of ecology on the evolution of a secondary sexual character due to sexual selection. Selection pressures imposed by seasonality of resources and environmental conditions affecting locomotion may have led to sexual selection via mating systems for females, and counter morphological adaptations of long penis bones in males. [ABSTRACT FROM AUTHOR]