Abstract
The aim of this study was to qualify the sexual size dimorphism at the both inter and intra-population levels of a copepod species, Cyclops vicinus, populations living in a small-scale geographical range. Sexual size dimorphism is evaluated by the ratio of female to male total length. But, to deep insight into sexual size dimorphism we assumed that the more difference between same measurements on the body from different sexes lead to more sexual dimorphism rate. The samples were taken from four water sources locating east and south-east part of Turkey. The significant inter and intra population differences were detected. The thorax width related measurements (mostly) and abdomen length had the most effective ones with changing order in the different populations on the sexual size dimorphism. Pearson correlation coefficients (r) showed that there were strong positive relationships between sexual dimorphism rate and predator presence (r = 0.88) and water volume of lake (r=0.72), while a moderate negative relationship both with water depth (r= -0.50) and with lake area (r= -0.45).
Highlights
Sexual size dimorphism (SSD) is a widespread phenomenon among animal groups (Fairbairn 1997; Blanckenhorn 2005) including the Copepoda, which are the most abundant metazoans on Earth (Humes 1994), and play an important role in aquatic food webs
This behavioural asymmetry may have led to the evolution of sexual dimorphism in copepods
It was clearly observed that the thorax width related (TW4, TW3, TW1) had the most effective measurements with changing order in the different populations on the sexual size dimorphism
Summary
Sexual size dimorphism (SSD) is a widespread phenomenon among animal groups (Fairbairn 1997; Blanckenhorn 2005) including the Copepoda, which are the most abundant metazoans on Earth (Humes 1994), and play an important role in aquatic food webs. Planktonic copepods show sexually dimorphic traits, inthat their males are generally smaller than females (Gilbert and Williamson 1983; Ohtsuka and Huys 2001; van Someren Gréve et al 2017). The higher relative size of female copepods may reflect their greater role in reproduction and posterity, especially in species that carry eggs during their development (Gilbert and Williamson 1983). Males are adapted for its locating role and its success can be enhanced through signals provided by the female. This behavioural asymmetry may have led to the evolution of sexual dimorphism in copepods. Dimorphic appendages and structures are engaged in (1) mate recognition by males; (2) capture of the female by the male; (3) transfer and attachment of a spermatophore to the female by the male; (4) removal of discharged spermatophore(s) by the female; and (5) fertilization and release of the eggs by the female (Blades 1977; Blades and Youngbluth 1979; Jacoby and Youngbluth 1983; Vaupel Klein 1998)
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