Population Structure of Canarium Labiatum (Röding, 1798) (Mollusca: Neostromboidae: Strombidae) on Green Island, Great Barrier Reef, Queensland
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Population Structure of Canarium labiatum (Röding, 1798) (Mollusca: Neostromboidae: Strombidae) on Green Island, Great Barrier Reef, Queensland Stephen J. Maxwell1, Misha K. Rowell2, Linda C. Hernandez Duran3, and Tasmin L. Rymer4 Abstract Canarium labiatum is a small gastropod of the Strombidae family that is commonly encountered in the inter-tidal zones of tropical Queensland, Australia, yet little is known of its population structure. A targeted survey of the Canarium labiatum population on Green Island, located near Cairns, Queensland, was conducted on 12 August 2015. Ninety adult specimens were collected, of which 49 were female and 41 were male. The sample demonstrated significant sexual axial- length size dimorphism, with a bias towards larger females. While we collected more females than males, this did not represent a statistically significant bias, and rather may reflect the clustering nature of the sample. In addition, there was no evidence of pseudohermaphroditism in females within the population under consideration. Interestingly, 11.1% of the sample did not show banding and brown/grey-blue maculations on a light grey shell, the typical colour pattern associated with Canarium labiatum. This paper fills a knowledge gap in Queensland’s Canarium labiatum population structure and provides a basis for a wider study into the size dynamics of Strombidae in general, but Canarium in particular. Keywords: Canarium labiatum, clustering, colour, imposex, pseudohermaphroditism, sex bias, size dimorphism 1 College of Science and Engineering, James Cook University, Cairns, QLD 4870, Australia (Email: [email protected]) 2 College of Science and Engineering and Centre for Tropical Environmental and Sustainability Sciences, James Cook University, Cairns, QLD 4870, Australia (Email: [email protected]) 3 College of Science and Engineering and Centre for Tropical Environmental and Sustainability Sciences, James Cook University, Cairns, QLD 4870, Australia (Email: [email protected]) 4 College of Science and Engineering and Centre for Tropical Environmental and Sustainability Sciences, James Cook University, Cairns, QLD 4870, Australia ([email protected]) Introduction 2004). The shells of individuals within a population Strombidae Rafinesque, 1815 is a frequently encoun- may vary greatly, with occasional examples hav- tered marine gastropod family common to most ing rare colour phenotypes (Abbott, 1960). Some tropi cal oceans. Members of the Strombidae express species, such as Strombus pugilis Linné, 1758 (Reed, sexually dimorphic characteristics in both physi o- 1993b) have demonstrated that there are more than logy and shell morphometrics, particularly in rela- two sexes within a population, with the reporting tion to the mean body size and length of the adult of masculinised females, a condition referred to as shell (Abbott, 1949, 1960, 1961; Reed, 1993a; Mutlu, pseudohermaphroditism, or imposex, and defined This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence. Individual articles may be copied or downloaded for private, scholarly and not-for-profit use. Quotations may be extracted provided that the author and The Royal Society of Queensland are acknowledged. Queries regarding republication of papers, or parts of papers such as figures and photographs, should be addressed to the Secretary of The Royal Society of Queensland ([email protected]). PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND VOL. 128 13 14 STEPHEN J. MAXWELL, MISHA K. ROWELL, LINDA C. HERNANDEZ DURAN, AND TAsmIN L. RYMER as the imposition of male sexual characteristics on compared to masculinised females, which were females in gastropods (Jenner, 1979; Nicolaus & larger in all size traits (Reed, 1995). However, Reed Barry, 2015). There is little or no knowledge regard- (1993b) found no evidence for this state in Lobatus ing any of these population characteristics in mem- costatus (Gmelin, 1791) after the examination of 500 bers of the stromboid genus Canarium Schumacher, specimens, suggesting an absence of masculinised 1817, worldwide, with most work having been con- females. Interestingly, there is no information on the ducted during the mid to late twentieth century on presence of pseudohermaphroditism in Canarium. taxonomy and basic physiology (Abbott, 1949, 1960, Another population dynamic that has remain 1961; Geary & Allmon, 1990; Reed, 1993a). unexplored in many Strombidae is the occurrence Evidence from fossil beds and large collections of colour morphs. Rare colour phenotypic expres- of extant taxa indicate that sexual axial-length size sion is well documented in the Strombidae (Kreipl dimorphism in Strombidae is a pleisiomorphic state, et al., 1999). However, the relative abundance of with a strong bias towards larger females (Geary & these colour forms within a population has not been Allmon, 1990). Strombidae vary greatly in the mean fully explored in many species. While some species size of adults within a population, and in the expres- are famous for their variability, such as Canarium sion of sexual dimorphic characteristics in both urceus (Linné, 1758) which can be found in all physiology and shell morphometrics (Abbott, 1949, colours of the rainbow and blends of those pri- 1960, 1961; Reed, 1993a; Mutlu, 2004; Arularasan maries (Abbott, 1960), other species have limited et al., 2011). However, it is necessary to explore the phylotypic plasticity in colouration. For example, phenomenon of sexual dimorphism in novel taxa Canarium klineorum Abbott, 1960 changes in within the wider Neostromboidae (Maxwell et al., shade and depth of colour, but there is limited vari- 2019) to establish the extent of this phylogenetic ability in the base colour of this taxon. The level constant within the wider clade. Greater understand- of colour variation within many Canarium popula- ing of the phenomena of sexual size dimorphism tions in Queensland is not yet known. will inform on the evolutionary limitations of size One such overlooked species, Canarium labia divergence. tum (Röding, 1798), is a gregarious and locally com- The extent of pseudohermaphroditism expres- mon species across its known range of the Central sion in Queensland’s Strombidae is another area Indo- and Eastern Pacific with typical banding and that has not been explored. In Strombidae, pseudo- brown/grey-blue maculations (Abbott, 1960). This hermaphroditism is often associated with the super- species has a high tolerance for environmental vari- imposition of a penis onto females (Reed, 1993b; ability, such as temperature, indicated by the extent Cardenas et al., 2005). The presence of pseudo her- of its range from the equatorial shallow waters past ma phroditism has varying effects on taxa, ranging the 30° latitudes (Abbott, 1960). It is also found in from sexual impotence to no physio logical effect a diverse range of habitats, from coral outer reefs on reproductive biology (Vlasconcelos et al., 2006). (Sudbury Cay, Queensland) to near-coastal muddy In masculinised female Strombus pugilis, the size rocky reefs (Yule Point, Queensland). of the dysfunctional external male sexual organ This paper has four aims that will elucidate the ranges from 2–12 mm, with no difference in ovarian knowledge gap concerning the life history and popu- structure between masculinised and normal females lation characteristics of a discrete population sample (Reed, 1993a). The presence of this penile gland in of Canarium labiatum on Green Island, Queensland, Strombus pugilis has no effect on the sexual func- Australia. The first seeks to test whether there is tion of the masculinised female as it is located on sexual size dimorphism in shell length. The second the edge of the egg groove (Reed, 1993b). Males examines sex ratios to determine whether there is a and normal females are smaller than masculin- sex-ratio bias. The third examines the expression of ised females when considering both size and shell phenotypic plasticity in shell colouration within the to body mass ratios (Reed, 1993b; Cardenas et sample. The fourth seeks to establish whether there al., 2005). For example, in Conomurex luhuanus is preliminary evidence of pseudohermaphroditism (Linné, 1758) populations, shell size of males was within the Canarium labiatum population under larger than normal females, but lighter in mass consideration. POPULATION STRUCTURE OF CANARIUM LABIATUM ON GREEN ISLAND 15 Abbreviations population were collected within the defined area AM – Australian Museum, Sydney, New South using a secondary fingertip search for four hours. Wales The type of clustering may affect the distribution QM – Queensland Museum, Brisbane, of sex ratios between males and females. Within con- Queensland gregations of the same taxon, four distinct categories QV – Queen Victoria Museum & Art Gallery, for clustering can be discerned: mixed age; juvenile; Launceston, Tasmania mating; and non-mating clusters (Brownell, 1977; SM – Collection of Stephen J. Maxwell, Cairns, Catterall & Poiner, 1983). Therefore, it is important Queensland to note the clustering nature of the sample on collec- tion, particularly the age demographic and presence Methods of sexual activity, as this may affect whether a sex- A targeted survey of a Canarium labiatum popu- ratio bias is observed or not. lation located near Cairns, Queensland, Aust ra- After collection, the total axial length of each lia (16°46′S, 145°58′E) was conducted by SM on specimen was measured. The animal