Shape Variation in Neotropical Cytheridella (Ostracoda) Using Semilandmarks-Based Geometric Morphometrics: A Methodological Approach and Possible Biogeographical Implications

Abstract

Geometric morphometrics offer effective methods to obtain information about shape and shape variability. In ostracodology, landmark-based methods are, however, not well established. To test the applicability of geometric morphometric analyses for ostracods, we investigated shape variation among recent and fossil populations of the genus Cytheridella using a combination of landmarks and semilandmarks. The study focuses on the species' intraspecific morphological variability on a supra-regional scale, comparing living populations from Florida, Yucatán, Colombia and Brazil. We performed Generalized least-squares Procrustes Analysis on 508 adult and juvenile specimens (valves) including stages A-1 to A-4. The analyses show that the primary pattern in shape variation is ontogenetic allometry, supporting a clear separation of adults and juveniles. Shape changes are relatively small during ontogeny from A-4 to A-1. Greatest modification of valve shape occurs during the last molt phase. Insufficient differentiation of sexes is caused by females with less developed brood pouches. Disentangling size- and non-size-dependent shape changes reveals regional differences between populations of the species C. ilosvayi and supports its taxonomic distinction from a fossil relative (C. danielopoli). The distribution of regional morphotypes of C. ilosvayi in Florida, Mexico, and Brazil are congruent with fly ways of water birds.

Evidence for Male Horn Dimorphism and Related Pronotal Shape Variation in Copris lunaris (Linnaeus, 1758) (Coleoptera: Scarabaeidae, Coprini)

“…We applied the geometric morphometrics semilandmark-based approach [ 43 , 44 , 45 , 46 , 47 , 48 , 49 ] to describe the overall shape variation of head and pronotum. The software tpsDig v2.31 [ 50 ] and tpsUtil v1.76 [ 51 ] ( ) were used to define the point configurations ( Figure 1 c,d) of the head (N H = 13) and pronotum (N P = 22).…”

Impact of climate and hydrochemistry on shape variation – a case study on Neotropical cytheroidean Ostracoda

“…Right and left valves were investigated separately due to 15 dimorphism in size and shape (Wrozyna et al, 2014). Beyond that, females and males were analyzed separately because a large part of within-valve variation has been shown to depend on sexual differences (such as the presence of brood pouches in females; Wrozyna et al, 2016).…”

“…Carapace outline was defined by two curves between LM 7 and 8, each comprising 30 equidistantly spaced semilandmarks ( Fig. 2; see also Wrozyna et al, 2016).…”

Significance of climate and hydrochemistry on shape variation – a case study on Neotropical cytheroidean Ostracoda

“…Both shortened and elongated morphotypes co-occur in one lake (i.e. Punta Laguna) (Wrozyna et al, 2018a). On the one hand, this co-occurrence could suggest the presence of microhabitats with specific environmental conditions, suggesting different impacts on valve calcification in the very same ecosystem.…”

“…The subject of study is the valves of the Neotropical cytheroidean ostracod species, Cytheridella ilosvayi. Studies by von Daday (1905) and Wrozyna et al (2016Wrozyna et al ( , 2018a already demonstrated considerable biogeographical variation in valve morphology among Floridian, Mexican, and Brazilian populations of that species. Morphological differences in populations of C. ilosvayi are discernible in both valves and appendages, adult and juvenile (A-1 to A-3) stages, and across sexes, suggesting that morphological divergence is a result of long-term biogeographic isolation (Wrozyna et al, 2018b).…”