Ecogeographical and Phylogenetic Effects on Craniofacial Variation in Macaques

伊藤毅，西村剛，高井正成

マカク属霊長類の顔の形には顕著な種間変異が見られるが，アロメトリー（サイズと連動した形の変化）の影響により，その適応的・系統的意味を読み解くことは困難だった．我々は，幾何学的形態測定という方法を用いることで，顔の形態情報をサイズ・アロメトリック形状成分・ノンアロメトリック形状成分に分割し，それぞれがどのように生態地理的・系統的要因によって説明されるかを検討した．サイズは，寒冷地ほど大きくなり，ベルクマンの法則に従った．アロメトリック形状成分（サイズが大きな個体ほど面長になる傾向）の様態は，生息環境間で差が見られた．つまり，比較的寒冷な環境に分布する種は，熱帯に分布する種に比べて，一般的なアロメトリーから予測されるよりも相対的に顔が短いことが示された．この形状変化は，マカク属内の異なる系統群で独立に複数回生じたと推定され，気候に関連した何らかの適応を反映すると考えられた．一方，ノンアロメトリック成分の一部（頬骨や上顎骨に見られた局所的な形状変異）は，系統関係を比較的よく反映することが示された．従来マカク化石の系統的位置に関する議論が混乱していたのは，気候環境に対する適応的収斂が顔の形の全体的な印象を実際の系統関係とは全く異なったものにしていたからなのかもしれない．今後，相同と考えれる形質のみを用いて化石種の系統関係を見直していく必要があるだろう．

American Journal of Physical Anthropology 2014 DOI: 10.1002/ajpa.22469

The widespread and complex ecogeographical diversity of macaques may have caused adaptive morphological convergence among four phylogenetic subgroups, making their phylogenetic relationships unclear. We used geometric morphometrics and multivariate analyses to test the null hypothesis that craniofacial morphology does not vary with cogeographical and phylogenetic factors. As predicted by Bergmann’s rule, size was larger for the fascicularis and sinica groups in colder environments. No clear size cline was observed in the silenus and sylvanus groups. An allometric pattern was observed across macaques, indicating that as size increases, rounded faces become more elongated. However, the elevation was differentiated within each of the former two groups and between the silenus and sylvanus groups, and the slope decreased in each of the two northern species of the fascicularis group. All allometric changes resulted in the similar situation of the face being more rounded in animals inhabiting colder zones and/or in animals having a larger body size than that predicted from the overarching allometric pattern. For non-allometric components, variations in prognathism were significantly correlated with dietary differences; variations in localized shape components in zygomatics and muzzles were significantly correlated with phylogenetic differences among the subgroups. The common allometric pattern was probably influenced directly or indirectly by climate-related factors, which are pressures favoring a more rounded face in colder environments and/or a more elongated face in warmer environments. Allometric dissociation could have occurred several times in Macaca even within a subgroup because of their wide latitudinal distributions, critically impairing the taxonomic utility of craniofacial elongation.

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