Myoglobin primary structure reveals multiple convergent transitions to semi-aquatic life in the world's smallest mammalian divers
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Curated by eLife
Evaluation Summary:
This study, based on an elaborated animal sample collection, reconstructs a comprehensive tree of Eulipotyphla, especially concentrating on Talpidae (moles), and infers the transitions of their lifestyles. It also models myoglobin structure and calculate electrophoretic mobility, demonstrating that semiaquatic eulipotyphlans have a higher net surface charge than fossorial, semifossorial, and terrestrial relatives. This variable myoglobin property indicates convergent shifts to a semi-aquatic lifestyle in multiple independent lineages including three separate times by ‘water shrews’, the smallest endothermic divers.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. The reviewers remained anonymous to the authors.)
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Abstract
The speciose mammalian order Eulipotyphla (moles, shrews, hedgehogs, solenodons) combines an unusual diversity of semi-aquatic, semi-fossorial, and fossorial forms that arose from terrestrial forbearers. However, our understanding of the ecomorphological pathways leading to these lifestyles has been confounded by a fragmentary fossil record, unresolved phylogenetic relationships, and potential morphological convergence, calling for novel approaches. The net surface charge of the oxygen-storing muscle protein myoglobin (Z Mb ), which can be readily determined from its primary structure, provides an objective target to address this question due to mechanistic linkages with myoglobin concentration. Here, we generate a comprehensive 71 species molecular phylogeny that resolves previously intractable intra-family relationships and then ancestrally reconstruct Z Mb evolution to identify ancient lifestyle transitions based on protein sequence alone. Our phylogenetically informed analyses confidently resolve fossorial habits having evolved twice in talpid moles and reveal five independent secondary aquatic transitions in the order housing the world’s smallest endothermic divers.
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Author Response:
Evaluation Summary:
This study, based on an elaborated animal sample collection, reconstructs a comprehensive tree of Eulipotyphla, especially concentrating on Talpidae (moles), and infers the transitions of their lifestyles. It also models myoglobin structure and calculate electrophoretic mobility, demonstrating that semiaquatic eulipotyphlans have a higher net surface charge than fossorial, semifossorial, and terrestrial relatives. This variable myoglobin property indicates convergent shifts to a semi-aquatic lifestyle in multiple independent lineages including that of the Russian desman, the smallest endothermic diver.
We note that the final sentence contains a misconception as the Russian desman – which weighs 180-220 g – is in fact the largest semi-aquatic member of the eulipotyphlan clade; a relative size …
Author Response:
Evaluation Summary:
This study, based on an elaborated animal sample collection, reconstructs a comprehensive tree of Eulipotyphla, especially concentrating on Talpidae (moles), and infers the transitions of their lifestyles. It also models myoglobin structure and calculate electrophoretic mobility, demonstrating that semiaquatic eulipotyphlans have a higher net surface charge than fossorial, semifossorial, and terrestrial relatives. This variable myoglobin property indicates convergent shifts to a semi-aquatic lifestyle in multiple independent lineages including that of the Russian desman, the smallest endothermic diver.
We note that the final sentence contains a misconception as the Russian desman – which weighs 180-220 g – is in fact the largest semi-aquatic member of the eulipotyphlan clade; a relative size comparison of this species relative to three other eulipotyphlans is presented in figure 1. The title of ‘the world’s smallest endothermic diver’ is instead held by the 12-18 g American water shrew.
We have reworked the text to avoid any future ambiguity here, and additionally recommend re-writing this sentence as:
“This variable myoglobin property indicates convergent shifts to a semi-aquatic lifestyle in multiple independent lineages including three separate times by ‘water shrews’, the smallest endothermic divers.”
Reviewer #1:
The authors of this study investigated the evolutionary process of the mammalian group of species including moles, shrews, hedgehogs, and solenodons with molecular approaches, with a reference to their diverse lifestyles. They first unveiled the among-species relationships and the chronological pattern of diversification by comparing molecular sequences of commonly shared genes. The highlight of the study is the inference of net surface charge and three-dimensional structure of the oxygen-storing muscle protein myoglobin, which reflected the varied lifestyles, with the Russian desman, the smallest endothermic diver, exhibiting a prominently altered disposition of myoglobin, possibly resulting from the adaptation to a semi-aquatic lifestyle.
As with the Evaluation Summary above, the final sentence contains a misconception regarding the Russian desman. We thus recommend re-writing this sentence as:
“The highlight of the study is the inference of net surface charge and three-dimensional structure of the oxygen-storing muscle protein myoglobin, which reflected the varied lifestyles, with three separate lineages of ‘water shrews’, the smallest endothermic diving species, exhibiting a prominently altered disposition of myoglobin, possibly resulting from the adaptation to a semi-aquatic lifestyle.”
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Reviewer #2 (Public Review):
This paper constructs one of the most comprehensive phylogenetic analyses of Eulipotyphla to date, using 23 genes from Meredith et al. (2011), especially concentrating on Talpidae (moles). The authors use this phylogenetic hypothesis to reconstruct lifestyle among eulipothphylans with the aim of understanding transitions to a semi-aquatic lifestyle. The authors also model myoglobin structure and calculate electrophoretic mobility, demonstrating that semiaquatic eulipotyphlans have a higher net surface charge than fossorial, semifossorial, and terrestrial relatives. They reconstruct the evolution of myoglobin using the time-calibrated tree of Eulipotyphla and infer 5 convergent increases in myoglobin net surface charge that correlate with semiaquatic lineages. The authors discuss the implications of this, …
Reviewer #2 (Public Review):
This paper constructs one of the most comprehensive phylogenetic analyses of Eulipotyphla to date, using 23 genes from Meredith et al. (2011), especially concentrating on Talpidae (moles). The authors use this phylogenetic hypothesis to reconstruct lifestyle among eulipothphylans with the aim of understanding transitions to a semi-aquatic lifestyle. The authors also model myoglobin structure and calculate electrophoretic mobility, demonstrating that semiaquatic eulipotyphlans have a higher net surface charge than fossorial, semifossorial, and terrestrial relatives. They reconstruct the evolution of myoglobin using the time-calibrated tree of Eulipotyphla and infer 5 convergent increases in myoglobin net surface charge that correlate with semiaquatic lineages. The authors discuss the implications of this, including the use of myoglobin reconstructions to infer lifestyle at selected nodes.
There are really very few things bad to say about this paper and highly recommend this paper for publication with only very minor changes. Overall it is a very well-written paper, and terrific contribution to studies of mammalian molecular evolution, myoglobin evolution, and eulipotyphlan phylogenetics.
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Reviewer #1 (Public Review):
The authors of this study investigated the evolutionary process of the mammalian group of species including moles, shrews, hedgehogs, and solenodons with molecular approaches, with a reference to their diverse lifestyles. They first unveiled the among-species relationships and the chronological pattern of diversification by comparing molecular sequences of commonly shared genes. The highlight of the study is the inference of net surface charge and three-dimensional structure of the oxygen-storing muscle protein myoglobin, which reflected the varied lifestyles, with the Russian desman, the smallest endothermic diver, exhibiting a prominently altered disposition of myoglobin, possibly resulting from the adaptation to a semi-aquatic lifestyle.
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Evaluation Summary:
This study, based on an elaborated animal sample collection, reconstructs a comprehensive tree of Eulipotyphla, especially concentrating on Talpidae (moles), and infers the transitions of their lifestyles. It also models myoglobin structure and calculate electrophoretic mobility, demonstrating that semiaquatic eulipotyphlans have a higher net surface charge than fossorial, semifossorial, and terrestrial relatives. This variable myoglobin property indicates convergent shifts to a semi-aquatic lifestyle in multiple independent lineages including three separate times by ‘water shrews’, the smallest endothermic divers.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. The reviewers remained …
Evaluation Summary:
This study, based on an elaborated animal sample collection, reconstructs a comprehensive tree of Eulipotyphla, especially concentrating on Talpidae (moles), and infers the transitions of their lifestyles. It also models myoglobin structure and calculate electrophoretic mobility, demonstrating that semiaquatic eulipotyphlans have a higher net surface charge than fossorial, semifossorial, and terrestrial relatives. This variable myoglobin property indicates convergent shifts to a semi-aquatic lifestyle in multiple independent lineages including three separate times by ‘water shrews’, the smallest endothermic divers.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. The reviewers remained anonymous to the authors.)
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