Reversed Sexual Size Dimorphism in the Ryukyu Scops Owl Otus elegans on Minami-Daito Island

Sawada, Akira; Iwasaki, Tetsuya; Matsuo, Taro; Akatani, Kana; Takagi, Masaoki

doi:10.2326/osj.20.15

Cited by 8 publications

(13 citation statements)

References 39 publications

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“…There is no significant sexual difference in annual survival rate (Sawada, Iwasaki, Inoue, et al, 2021 ). The average body mass of adult males and adult females are 88.4 and 92.2 g, respectively, showing slight reversed sexual size dimorphism (Sawada, Iwasaki, Matsuo, et al, 2021 ).…”

Section: Methodsmentioning

confidence: 99%

“…Wing length (to the nearest 0.5 mm) was measured with a stainless‐steel ruler. Measurements were made twice or more during each capture, allowing the use of mean values (see Table 1 ; Sawada, Iwasaki, Matsuo, et al, 2021 ). Since the correlations of these variables were weak, the values of the variables were used in the analysis as they were (Figure S1 ).…”

Section: Methodsmentioning

confidence: 99%

“…Sex was determined by vocal characteristics, by the presence of a brood patch, or by PCR amplification of the Chromo Helicase DNA‐binding gene (Fridolfsson & Ellegren, 1999 ; Sawada, Iwasaki, Matsuo, et al, 2021 ; Takagi, 2020 ). Age class (yearling or adult) was estimated from plumage characteristics following Sawada, Iwasaki, Matsuo, et al ( 2021 ). Age, as used in the analyses below, refers to this dichotomous classification and not an exact age in years.…”

Section: Methodsmentioning

confidence: 99%

“…In brief, if a bird meets two criteria out of three (pointed primaries, soft primary rachides, and worn secondaries), we judged the bird yearling. Detailed procedures for sexing and aging the owls are described in Sawada, Iwasaki, Matsuo, et al ( 2021 ).…”

Section: Methodsmentioning

confidence: 99%

“…Here, we address the existence of assortative mating and the generating mechanism of it in the Ryukyu Scops Owl Otus elegans interpositus , a species in which males are slightly smaller than females (Sawada, Iwasaki, Matsuo, et al, 2021 ). During the long‐term (since 2002) monitoring of an isolated population of this taxon, data have been accumulated on the morphology, reproductive success, territories, and age of breeding pairs.…”

Section: Introductionmentioning

confidence: 99%

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Mate choice for body size leads to size assortative mating in the Ryukyu Scops Owl Otus elegans

Sawada

Iwasaki

Akatani

et al. 2022

Ecology and Evolution

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Understanding evolutionary phenomena that involve size assortative mating requires elucidating the generating mechanisms on which assortment is based. Although various mechanisms have been suggested, their relative importance may differ across taxonomic groups. Males selecting for large, fecund females combined with the dominance of large males in the competition for females has been suggested as a major mechanism in specific groups. However, raptors do not appear to conform to this, because the selection for smallness among males (assumed in a theory of reversed sexual size dimorphism) and the selection for largeness among males (assumed in the theory of size assortative mating) are in opposite directions. We studied the assortative mating during a long‐term study of the Ryukyu Scops Owls Otus elegans interpositus . Significant assortative mating was found for culmen length (from the base to the tip of the bill) and wing length (from the bend of the wing to the tip of the longest primary). Statistical control of the spatial and temporal accessibility of potential mates did not affect the assortment. Males with short wings had slightly higher fitness components than those with long wings, and females settling early tended to have small wings. Considering that early‐settling females can preferentially choose their mates, these results suggest that smaller females have an advantage when choosing smaller males with good reproductive performance. Improved flying and hunting ability of smaller individuals may be the background of choosing smaller individuals. We propose that, not passive process like similarity between individuals and their potential mates, but active mate choice for small individuals is an explanation for the assortative mating in this owl.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mate choice for body size leads to size assortative mating in the Ryukyu Scops Owl Otus elegans

Sawada

Iwasaki

Akatani

et al. 2022

Ecology and Evolution

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Extreme natural size variation in both sexes of a sexually cannibalistic mantidfly

et al. 2022

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In sexually cannibalistic animals, the relative sizes of potential mates often predict the outcome of aggressive encounters. Mantidflies are spider egg predators as larvae and generalist predators as adults. Unlike most cannibalistic species, there is considerable individual variation in body size in both sexes. Using preserved collections of Dicromantispa sayi , we focused on three body size metrics that we found to be positively correlated and accurately measured across researchers. We found extreme size variation in both sexes: the largest 10% of females were 1.72× larger than the smallest 10%, and the largest 10% of males were 1.65× larger than the smallest 10%. On average, females were 7.94% larger than males. In exploring possible causes of this variation, we uncovered differences among populations. To explore the effect of spider egg sac size on adult mantidfly size, we reared mantidfly larvae on egg sacs from two jumping spider species with small or large egg sacs. Mantidfly larvae reared on small egg sacs were smaller than those reared on large egg sacs. This study provides the groundwork to design ecologically relevant experiments exploring the causes and consequences of extreme size variation in an understudied system with intriguing natural history.

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Estimation of Population Size and Sex Ratio of Ryukyu Scops Owl Otus elegans on Hateruma Island

Sawada

2022

Ornithological Science

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Reversed Sexual Size Dimorphism in the Ryukyu Scops Owl Otus elegans on Minami-Daito Island

Cited by 8 publications

References 39 publications

Mate choice for body size leads to size assortative mating in the Ryukyu Scops Owl Otus elegans

Mate choice for body size leads to size assortative mating in the Ryukyu Scops Owl Otus elegans

Extreme natural size variation in both sexes of a sexually cannibalistic mantidfly

Estimation of Population Size and Sex Ratio of Ryukyu Scops Owl Otus elegans on Hateruma Island

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