Comparative penile morphology of East African galagos of the genus Galagoides (family Galagidae) implications for taxonomy.код для вставкиСкачать
American Journal of Primatology 69:16–26 (2007) RESEARCH ARTICLE Comparative Penile Morphology of East African Galagos of the Genus Galagoides (Family Galagidae): Implications for Taxonomy ANDREW PERKIN Nocturnal Primate Research Group, Oxford Brookes University, Reading, United Kingdom Recent studies on the comparative penile morphology of galagos have revealed complex patterns that vary among both genera and species, and help with species identification. So far the penile morphologies of 14 galago species have been described and an identification key has been proposed. The present study extends and revises previous work. Wild Galagoides cocos, G. granti, G. zanzibaricus and G. rondoensis from the Eastern Arc Mountains and coastal forests of Tanzania and Kenya were live-trapped, and one species (G. orinus) was examined using a museum specimen. Penile morphology was photographed, traced, and described qualitatively. All of the mature males had penile spines. Spines were absent or indistinct in immature males of all of the species. The penile morphologies of G. cocos, G. granti, and G. zanzibaricus are similar in their overall distribution and type of spines, but differ in the shape of the glans penis. Both G. orinus and G. rondoensis have divergent penile morphologies compared to all other galagos, and are probably phylogenetically distinct. The results support other recent morphological and behavioral studies that consider these five galagos to be distinct species. The evolution of the baculum and spines is thought to be linked to sexual selection in multimale mating systems, but the mechanisms involved are not entirely understood. Adult male G. rondoensis appear to display the penile spines by exposing the distal section of the penis. Am. J. Primatol. 68:16–26, 2007. c 2006 Wiley-Liss, Inc. Key words: penile morphology; galago; spines; baculum; cryptic female choice; taxonomy Contract grant sponsor: Oxford Brookes University; Contract grant sponsor: Primate Conservation Inc.; Contract grant sponsor: Margot Marsh Biodiversity Fund; Contract grant sponsor: Tanzania Forest Conservation Group; Contract grant sponsor: Africa Rainforest Conservancy. Correspondence to: Andrew Perkin, 39A Rickman Close, Woodley, Reading, RG5 3LL UK. E-mail: firstname.lastname@example.org Received 29 July 2005; revised 24 January 2006; revision accepted 13 February 2006 DOI 10.1002/ajp.20323 Published online in Wiley InterScience (www.interscience.wiley.com). r 2006 Wiley-Liss, Inc. Penile Morphology in Galagoides / 17 INTRODUCTION There has been a recent increase in the number of galago species recognized, as new techniques are enabling primatologists to better understand the extent of the differences among these species, despite their cryptic morphology and behavior [Bearder, 1999; Groves, 2000; Grubb et al., 2003; Masters & Bragg, 2000; Honess & Bearder, 1996; Nash et al., 1989]. The separation of species has been aided by research on vocal repertoires, with different vocal profiles correlating with differences in hand-pad structure, genetic diversity, reproductive anatomy, and facial markings [Anderson et al., 2000; Bayes, 1998; Bearder et al., 2006; Fjeldså et al., 2005; Masters et al., 2005]. The superficial similarity in morphological characters of galagos may be due to extensive convergence [Bearder, 1999]. Comparative studies of reproductive anatomy in primates have revealed complex and specialized genitalia [Anderson, 1998; Dixson, 1998, 1989; Hill, 1953]. Previous studies of galago penile anatomy have shown elaborate differences among species [Anderson, 1998, 2000; Dixson, 1995; Dixson & Van Horn, 1977; Hill, 1953]. They vary in shape and in the presence and distribution of hard, keratinized spines, as well as in the size, shape, and relative position of the baculum. Three spine types have been defined: 1) simple spines with a single point and moderate length; 2) robust spines that are single-pointed, enlarged structures, often thickened at the base; and 3) complex spines that are multipointed [Dixson, 1995]. The baculum can be prominently positioned and exposed, or just visible and surrounded by tissue structures of the glans penis. For species with spineless glans, the shape of the glans penis is diagnostic, while for species with spines, the relative size and the position of the spines on the penis vary among species [Anderson, 2000]. For example, studies of comparative penile morphology have revealed little intraspecific variation within Otolemur garnettii or O. crassicaudatus [Anderson, 1998, 2000]. Complex penile morphologies and the shape and size of the baculum in multimale/multifemale mating systems, such as those found in the galagos, may have evolved for two reasons: 1) to displace the sperm of other competitors, and 2) to ‘‘encourage’’ females to take up spermatozoa by the male placing ejaculate in the most advantageous position, or by stimulating uptake and transport of spermatozoa within the female’s tract [Dixson, 1998]. This may lead to the penis functioning as an ‘‘internal courtship device’’ [Eberhard, 1996]. The different spine types found in galago penises may be related to the different roles that each spine type may perform. Type 2 spines may have a role in mate-guarding, while Type 1 spines may influence physiological feedback [Dixson, 1998]. While the reasons for this are not fully understood, it is speculated that penile morphological variation may be the result of speciation events influenced by sexual selection via cryptic female choice [Dixson, 1998]. The penile morphologies of 14 galago species have been described, including the East African dwarf galago species Galagoides zanzibaricus, G. udzungwensis, G. granti, and G. rondoensis [Anderson, 2000]. However, since Anderson’s  study was published, taxonomic changes affecting these species have been made. G. cocos has been recognized as the correct name for the Kenya coast galago (often mistakenly referred to as G. zanzibaricus) [Butynski et al., in press], and G. udzungwensis has been subsumed into the taxonomy of G. zanzibaricus [Grubb et al., 2003]. This study provides a detailed comparison of five species: Galagoides cocos, G. zanzibaricus, G. granti, G. orinus, and G. rondoensis. These species occupy the globally important biodiversity hotspots of the Eastern Arc Mountains Am. J. Primatol. DOI 10.1002/ajp 18 / Perkin and the coastal forest mosaic of Tanzania and Kenya [Burgess & Clarke, 2000; Burgess et al., 2004]. MATERIALS AND METHODS Twenty-five galagos were photographed and measured to examine the details of their penile morphology. The study subjects included 21 live animals that were trapped from various localities in the Eastern Arc Mountains and coastal forests of Tanzania and Kenya, and four museum specimens. From this group, mature males (based on spine and testes development) were selected for analysis (Table I). Most of the galagos were trapped with the use of a Chardonneret trap [Charles-Dominique, 1977], and others were captured opportunistically with mist nets set for bats. Live galagos can be processed without the need for anesthetic if they are handled in a quiet environment. In the case of museum specimens, both the baculum and, in many cases, the penile spines survived wet and dry preservation. The testes and scrotum survive only wet preservation. Tracings were taken from each photograph and drawn to scale for direct comparison within and among species. The delineation of regions of the penis is adapted from Anderson , who divided the penis into three equal sections: distal, mid, and proximal. The qualitative characters for each species were described by section and included the 1) relative shape and size of the glans penis, 2) spine type (see Introduction), 3) distribution of spines, and 4) relative position of the baculum. Measurements of penis length were taken and in some cases the dorsoventral and lateral penis widths were taken from points on the proximal, mid-point, and distal parts of the penis. However, in contrast to Anderson’s  study, in which digital scanning technology enabled detailed quantitative calculations of glans and spine area to be made, here I describe the penile morphology qualitatively. When the galagos were captured, the amount by which the distal part of the penis protruded beyond the prepuce was also noted. Dixson  compared the baculum and glans penis length with body mass. In this study I determined a penis length to body mass ratio by dividing the species’ mean greatest penis length by the species’ mean body mass. The sample sizes were too small to conduct statistical analyses. I assessed ontogenetic development by comparing penile spine development with body size and testes development. In some cases the testes length and widths were also measured. RESULTS In all of the mature male galagos examined, the penises had various arrangements and types of backward-pointing spines; however, in immature males the spines were absent or only just visible (Table I, Figs. 1,2,3). When data were available, spine development was linked to the size and development of the testes. Species accounts are given below. Galagoides cocos The penile morphology of this species has not previously been described. Four specimens from three sites were examined, and only two of these were mature (Table I). The glans penis is cylindrical but enlarges slightly in the middle more dorsoventrally then laterally (Fig. 1). The mean lateral width at the penis base, mid-section, and tip was 2.0, 2.3, and 2.2 mm, respectively (n 5 2). The baculum protruded very little (o1 mm) from the glans penis in one specimen examined, but remained equal to the level of the glans penis in the other mature Am. J. Primatol. DOI 10.1002/ajp G. zanzibaricusa G. zanzibaricus G. zanzibaricusa G. zanzibaricus G. granti,a FMNH/ KMH 25830 G. granti,a FMNH/ KMH 25799 G. zanzibaricusa G. cocos G. cocos,a NMK, MR14 G. cocos Galagoides cocosa Species, museum, and specimen number given where relevant Diani FR, Kenya (coordinates: 0419S 3933E) Mgambo FR, Kenya (coordinates: 0445S 3848E ) Mgambo FR, Tanzania Mrima Hill FR, Kenya (coordinates: 0428S 3915E) Kichi Hills FR, Tanzania (coordinates: 0429S, 3916E) Lulanda FR, Tanzania (coordinates: 0707S 3623E) Pugu FR, Tanzania (coordinates: 0642S 3905E) Pugu FR, Tanzania Kazimzumbwi FR, Tanzania (coordinates: 0643S 3902E) Kazimzumbwi FR, Tanzania Pande GR, Tanzania (coordinates: 0642S 3905E) Locality 21.0 16.0 23.0 9.0 133.5 136.0 147.0 122.0 145.0 160.0 18.6 22.0 140.0 108.0 165.0 69.0 177.0 Mass (g) 21.0 20.0 23.0 18.0 21.5 Greatest penis length (mm) 10/9 5/5 NM TND 18/15 NM NM TND NM TND NM Scrotum greatest length/width (mm) Partly developed Not present Fully developed Not present Fully developed Fully developed Fully developed Not present Fully developed Not present Fully developed Penile spine development Mature Immature Mature Immature Mature Mature Mature Immature Mature Immature Mature Assessment of sexual maturity TABLE I. The Localities, Greatest Penis Length, Greatest Width, and Length of Scrotum, Body Mass and Presence of Spines of the Galagos Examined Penile Morphology in Galagoides / 19 Am. J. Primatol. DOI 10.1002/ajp Am. J. Primatol. DOI 10.1002/ajp zanzibaricusa rondoensis rondoensis rondoensisa rondoensisa rondoensisa rondoensisa rondoensis rondoensis Pande GR, Tanzania Mkungwe FR, Tanzania (coordinates: 0652S 3734E) Pugu FR, Tanzania Pugu FR, Tanzania Pugu FR, Tanzania Pugu FR, Tanzania Pugu FR, Tanzania Pugu FR, Tanzania Pugu FR, Tanzania Pugu FR, Tanzania Kazimzumbwi FR, Tanzania Kazimzumbwi FR, Tanzania Pande GR, Tanzania New Dabaga FR, Tanzania (coordinates: 0805S 3554E) Locality 25.0 12.8 26.0 18.2 11.0 11.0 24.0 26.0 22.0 20.0 9.0 12.0 21.5 8.0 11.0 Greatest penis length (mm) 80.0 97.0 65.0 150.0 71.0 52.0 62.0 72.0 61.0 81.0 54.0 57.0 177.0 60.0 111.0 Mass (g) Fully developed Fully developed Partly developed Fully developed Partly developed Not present Fully developed Fully developed Fully developed Fully developed Partly developed Partly developed Fully developed Not present Not present Penile spine development Mature Mature Mature Mature Immature Immature Mature Mature Mature Mature Immature Immature Mature Immature Immature Assessment of sexual maturity Animals compared in this study. FMNH, Field Museum of Natural History (Chicago); NMH, National Museums of Kenya; KMH, Collection number of Prof. K.M. Howell; FR, forest reserve; GR, game reserve; NM, not measured; TND, testes not descended (therefore not measured). a NM NM NM NM 13/10 TND 10/24 15/18 NM NM TND TND NM TND 3/3 Scrotum greatest length/width (mm) A level of sexual maturity is assessed on the basis of the presence of penile spines and testes development. G. rondoensisa G. orinus,a FMNH/ KMH 22496 G. rondoensisa G. G. G. G. G. G. G. G. G. Galagoides cocosa G. zanzibaricus G. zanzibaricus Species, museum, and specimen number given where relevant TABLE I. Continued 20 / Perkin Penile Morphology in Galagoides / 21 Fig. 1. Schematic drawings and relative sizes of the penile morphologies of 1) G. cocos, 2) G. granti, 3) G. zanzibaricus, 4) G. rondoensis, and 5) G. orinus (specimen FMNH/KMH 22496). A: Ventral view. B: Dorsal view. C: Lateral view (dorsum right). Scale is indicated on the right. specimen. The mean length of the penis is similar to G. zanzibaricus and G. granti, with a relative penis length index of 0.130 (n 5 2; Table II). There are no spines on the tip of the penis, but simple Type 1 spines start to emerge in the proximal half of the distal section. These develop into downward-pointing robust Type 2 spines that are found in the mid-section, and in the proximal section they reduce in size to Type 1 spines (Fig. 1). The spines are geometrically arranged in diagonal lines on the penis. The immature animals examined (n 5 2) had low body mass and no penile spines. One had a relatively long penis (20 mm) but no descended testes (Table I). Prior to examination it was noted that only the distal tip of the penis protruded from the foreskin. Am. J. Primatol. DOI 10.1002/ajp 22 / Perkin Fig. 2. Examples of an immature G. zanzibaricus with undeveloped spines (top: lateral profile), and a mature G. zanzibaricus penis with fully developed spines (bottom: dorsal profile). The baculum protrudes more prominently in mature males. A mature G. rondoensis (right) held after it was extracted from the trap, showing the prominent distal penile morphology display. Photos not to scale. [Color figure can be viewed in the online issue, which is available at www.interscience. wiley.com.] Fig. 3. Photographs of the penile morphology of G. rondoensis: (a) an immature male (lateral profile), (b) a mature male (lateral view), and (c) a mature male (dorsal view). Photos not to scale. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.] Galagoides granti Two mature individuals from different sites were examined (Table I). In both cases the penis was larger dorsoventrally (mean width at mid-section 5 5.52 mm) than laterally (mean width at mid-section 5 2.54 mm), giving a thin pointed appearance overall (Fig. 1). The baculum protrudes at a point ‘‘off center’’ toward the dorsal side of the penis. The mean length of the penis is similar to but shorter than that of G. cocos and G. zanzibaricus, and the relative penis length index is 0.133 (n 5 2; Table II). There are no spines around the penis tip, but Type 1 spines start to emerge in the proximal half of the distal section. Downwardpointing robust Type 2 spines cover the mid-section, with the highest densities on Am. J. Primatol. DOI 10.1002/ajp Penile Morphology in Galagoides / 23 TABLE II. Mean Penis Length and Body Mass of the Mature Galagos Examined and the Penis Length to Body Mass Ratios Compared for the Five Galagos Species Studied Species G. G. G. G. G. cocos granti zanzibaricus rondoensis orinus Mean greatest penis length (mm) Range (mm) Mean mass (g) Range (g) n Relative penis lengtha 22.25 20.50 21.05 23.60 12.80 21.5–23.0 18.6–21.5 18.2–23.0 20.0–26.0 12.8 171.00 150.00 143.90 70.16 97.00 165.0–177.0 140.0–160.0 133.5–150.0 61.0–80.0 97.0 2 2 4 6 1 0.130 0.133 0.146 0.342 0.132 G. rondoensis has a high penis length to body mass index. a Species mean greatest penis length/species mean body mass (see text and Table I). the lateral flanks and the dorsal section, and few on the ventral section. The spines continue partially into the proximal third and then disappear. The spines are geometrically arranged in lines on the penis. Prior to examination it was noted that only the distal tip of the penis protruded from the foreskin. Galagoides zanzibaricus Seven individuals from four different sites were examined, and five of these were considered mature (Table I). The penises of the mature individuals were cylindrical in shape, but expanded greatly laterally in the mid-portion of the penis (Figs. 1 and 2). The mean lateral width at the penis base, mid-section, and tip was 2.2, 3.5, and 2.1 mm respectively (n 5 3). Immature individuals were similar in shape, but expansion of the mid-section of the penis was less exaggerated. The baculum protrudes at a point off-center toward the dorsal side of the penis. The mean length of the penis is similar to G. cocos and G. granti, and the relative penis length index is 0.146 (n 5 5; Table II). There are no spines around the tip, but Type 1 simple spines start to emerge in the proximal half of the distal section. Downward-pointing robust Type 2 spines cover the mid-section completely. The spines on the dorsal side of the penis are arranged geometrically and longitudinally, and point slightly inward to a central line or crease down the middle of the penis, mostly in the mid-section (Figs. 1 and 2). The spine cover continues down into the proximal third of the penis on the dorsal surface, but it starts to reduce in size and spines are absent on the ventral and lateral surfaces. Immature animals of G. zanzibaricus with undescended or relatively small testes either have no spines, or they have a lower body mass and less-developed spines (Table I, Fig. 2). However, the gross shape of the glans penis remains consistently similar between immature and mature males. Prior to examination it was noted that only the distal tip of the penis protruded from the foreskin. Galagoides rondoensis Ten individuals from three sites were examined, and six of these were considered mature (Table I). G. rondoensis has a large and highly differentiated penis. The penis has a long narrow shaft in the proximal region (mean dorsoventral width 5 2 mm, n 5 6) and mid-sections (mean dorsoventral width 5 2 mm, n 5 6) before it expands and becomes ‘‘flute shaped’’ in the distal Am. J. Primatol. DOI 10.1002/ajp 24 / Perkin region (mean dorsoventral width 5 6.5 mm, n 5 6). The baculum is exposed at a point off-center toward the dorsal side of the penis of the glans penis, but is ‘‘nested’’ inside so that it does not protrude above the level of the glans. In comparison to the other species examined here, G. rondoensis has a remarkably large penis, resulting in a high relative penis length index of 0.342 (n 5 6; Table II). The penis has a cluster of Type 1 and 2 spines around the ventral and lateral portions of the tip. Two of the largest spines, one on each side, appear to protrude markedly at approximately 451 to the penis. The spines do not appear to be arranged geometrically. There are no spines present in the mid- and proximal regions. Spines are not present in immature animals with undescended or small testes, but small nodes or ‘‘buds’’ can be seen in the same areas where spines are formed in adults (Fig. 3). The relative spine development noted was thought to be related to different levels of maturity, with the greatest development occurring in individuals with larger bodies and testes. Upon capture the distal end of the penis and the ‘‘spinal array’’ were noted to be consistently exposed and visible above the foreskin in mature males (Fig. 2). Galagoides orinus The penile morphology of Galagoides orinus was previously undescribed. The current description is based on one specimen that, as far as we know, is the only male of this species in the museum collections. The specimen was judged to be mature, based on body measurements, body mass, and the presence of descended testes (Table I). G. orinus has a unique and differentiated penis morphology (Fig. 1). The overall shape of the penis is conical. The proximal section is narrow (dorsoventral width 5 2.1 mm) and widens through the mid-section (dorsoventral width 5 2.3 mm), and continues to widen to the distal end (dorsoventral width 5 3.2 mm) of the glans penis. G. orinus has a small penis in absolute terms, but its relative penis length index of 0.132 (n 5 1) is similar to that of G. cocos, G. zanzibaricus, and G. granti (Table II). On the dorsal surface of the proximal section there is a group of approximately 14 large Type 2 spines arranged in a regular pattern, but no spines are visible on the lateral and ventral sections. The mid-section is complex. The Type 2 spines continue to a mid-point and then there is an area with no spines. Small, geometrically positioned Type 1 spines cover the distal region up to the end of the glans penis. From the end of the glans penis, the baculum protrudes prominently and is positioned toward the dorsal edge. DISCUSSION The results of this study support the conclusion that penile morphology can be used to help identify galago species and aid in their classification. All of the species examined in this study had spined penises, a result that is contradictory to some of the findings of Anderson . This may indicate that the G. udzungwensis (now classified as G. zanzibaricus), G. granti, and G. rondoensis specimens illustrated in Anderson  were immature animals. Indeed, Honess  acknowledged that this may be the case for the G. rondoensis (n 5 1) and G. udzungwensis (n 5 1) individuals trapped in that study. G. cocos, G. granti, and G. zanzibaricus, which have undergone recent changes in taxonomic status, are superficially similar in body morphology and may be closely related species [Butynski et al., in press] (Perkin, unpublished data). This aspect is also indicated by similarities in their penile morphologies. The penile Am. J. Primatol. DOI 10.1002/ajp Penile Morphology in Galagoides / 25 morphologies of G. zanzibaricus examined in this study, sampled from mainland coastal sites, appear to differ from the description of the penile morphologies of G. udzungwensis (now renamed G. zanzibaricus) from Matundu Forest Reserve (ca. 250 km further inland to the southwest), indicating possible intraspecific variation [Anderson, 2000; Honess, 1996]. G. rondoensis is a highly distinctive species, both morphologically and behaviorally [Honess, 1996] (Perkin unpublished data). Equally, the penile morphology is highly distinctive in terms of relative length, shape, and spinal distribution. G. rondoensis is the only galago species in this study that always displayed the distal region of the penis when captured (Figs. 2 and 3). Whether this is display is detectable and registered by females prior to mating is an intriguing question. Judging from the one specimen examined, G. orinus has a unique penile morphology that is readily distinguishable from other galago species. This includes G. demidoff, of which G. orinus was once considered to be a subspecies [Grubb et al., 2003]. These taxa also differ from each other vocally and morphologically [Grubb et al., 2003; Honess & Bearder, 1996; Lawrence & Washburn, 1936; Perkin et al., 2002]. When describing galago penile morphology, investigators should consider the ontogeny, because immature males may exhibit no or undeveloped spines. The profile of the penis must be indicated for an accurate comparison of penile morphology. Further research and greater sample sizes are required before we can understand the levels of intra- and interspecies variation among galago penile morphologies. The roles of testes development and social organization in relation to penis ontogeny are also poorly understood. ACKNOWLEDGMENTS My thanks go to Professor S.K. Bearder, Dr. N. 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