Sexual shape dimorphism and selection pressure on males in fossil ostracodes

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doi: 10.1017/pab.2016.57
Author(s): Yamaguchi, Tatsuhiko; Honda, Rie; Matsui, Hiroki; Nishi, Hiroshi
Author Affiliation(s): Primary:
Kochi University, Center for Advanced Marine Core Research, Nankoku, Japan
Other:
Tohoku University, Japan
Volume Title: Paleobiology
Source: Paleobiology, 43(3), p.407-424. Publisher: Paleontological Society, Lawrence, KS, United States. ISSN: 0094-8373 CODEN: PALBBM
Note: In English. 71 refs.; illus., incl. 5 tables
Summary: Sexual dimorphism is thought to have evolved via selection on both sexes. Ostracodes display sexual shape dimorphism in adult valves; however, no previous studies have addressed temporal changes on evolutionary timescales or examined the relationships between sexual shape dimorphism and selection pressure and between sexual shape dimorphism and juvenile shape. Temporal changes in sexually dimorphic traits result from responses of these traits to selection pressure. Using the Gaussian mixture model for the height/length ratio, a valve-shape parameter, we identified sexual differences in the valve shape of Krithe dolichodeira s.l. from deep-sea sediments of the Paleocene (62.6-57.6 Ma) and estimated the proportion of females in the fossil populations at 11 time intervals. Because the proportion of females in a population is altered by the mortality rate of adult males, it is reflective of selection pressure on males. We attempted to correlate the height/length ratios between the sexes with the proportion of females, taking into consideration that the valve shape was not linked with the selection pressure on males. In time-series data of the height/length ratio, both sexes indicate no significant changes on evolutionary timescales, even though the sex ratio of the population changed from female skewed to male skewed during the late Paleocene. The sexual shape dimorphism was not driven by sexual selection. The static allometry between the height/length ratio and length indicates that the sexual shape dimorphism did not function for sexual display. The absence of change over time in the female allometric slope suggests that the evolution of valve shape was constrained by stasis.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 10 Paleontology, Invertebrate; Allometry; Arthropoda; Atlantic Ocean; Biologic evolution; Cenozoic; Crustacea; Expedition 342; Growth; IODP Site U1407; Integrated Ocean Drilling Program; Invertebrata; Krithe dolichodeira; Mandibulata; Microfossils; Morphology; North Atlantic; Ostracoda; Paleocene; Paleogene; Sexual dimorphism; Statistical analysis; Tertiary; Time series analysis
Coordinates: N412530 N412530 W0494847 W0494849
Record ID: 2017077590
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