Sperm Morphology in Neotropical Primates

Abstract

The morphological and morphometric characterization of spermatozoa has been used as a taxonomic and phylogenetic tool for different species of mammals. We evaluated and compared the sperm morphometry of five neotropical primate species: Alouatta caraya, Ateles belzebuth and Ateles chamek of family Atelidae; and Cebus cay (=Sapajus cay) and Cebus nigritus (=Sapajus nigritus) of family Cebidae. After the collection of semen samples, the following parameters were measured on 100 spermatozoa from each specimen: Head Length, Head Width, Acrosome Length, Midpiece Length, Midpiece Width and Tail Length. Considering the available literature on sperm morphometry, we gathered data of 75 individuals, from 20 species, 8 genera and 2 families. These data were superimposed on a phylogeny to infer the possible direction of evolutionary changes. Narrower and shorter spermatozoa seem to be the ancestral form for Cebidae, with a trend toward wider and larger heads in derived groups. The spermatozoa of Atelidae may show an increase in total length and midpiece length. Sperm heads would have become narrower in the more derived groups of Ateles. Sperm length may increase in the more derived species in both families. Our results are discussed in the context of sperm competition and sexual selection.

Keywords: Platyrrhini; sperm competition; sperm morphometry.

Figure 1

Microphotographs of spermatozoa from the studied neotropical primates. (a) Cebus cay (=Sapajus cay); (b) Cebus nigritus (=Sapajus nigritus); (c) Ateles belzebuth; (d) Ateles chamek; (e) Alouatta caraya.

Figure 2

Box plots for the morphometric measurements made on spermatozoa of the studied neotropical primates. (a) Head Length (HL); (b) Head Width (HW); (c) Acrosome Length (AL); (d) Midpiece Length (ML); (e) Tail Length (TL). The square within the box indicates the mean, the boxes indicates the standard deviation interval (±SD) and the and the ends of the vertical line indicate the maximum and minimum values. Cebus cay (CCY, =Sapajus cay); Cebus nigritus (CNI, =Sapajus nigritus); Ateles belzebuth (ABE); Ateles chamek (ACH); Alouatta caraya (ACA).

Figure 3

Evolution of sperm morphology and morphometry. Mean sperm measurements were superimposed on a phylogeny of neotropical primates (phylogeny from Dumas and Mazzoleni [33] with modifications [34,35,36,37,38,39]). When available, a scale diagram and/or microphotograph of the sperm head and proximal portion of the midpiece were provided for each species. Only species with data of head length and head width were included. HL: Head Length, HW: Head Width, AL: Acrosome Length, ML: Midpiece Length, TL: Total Length, Ellipt: Ellipticity = (HL/HW), Elong: Elongation = ((HL − HW)/(HL + HW)). Cebus cay = Sapajus cay; Cebus nigritus = Sapajus nigritus.