Seeing stars: a molecular and morphological investigation into the evolutionary history of Odontasteridae (Asteroidea) with description of a new species from the Galapagos Islands

Abstract

Odontasteridae (Asteroidea: Echinodermata) (Verrill in Am J Sci, 1899) is placed within Valvatida, a derived assemblage of sea stars. Odontasterids are found in the Southern, Atlantic, and Pacific Oceans and are concentrated in high southern latitudes. To date, the phylogenetic and evolutionary history of Odontasteridae as a whole has not been rigorously examined. We conducted molecular and morphological phylogenetic analyses of Odontasteridae to assess the interrelationships among and within recognized genera. We used mitochondrial 16S and cytochrome c oxidase subunit I molecular markers and 29 external morphological characters in an attempt to reconstruct the evolutionary history of the group. Generally, our results indicate that traditionally used external skeletal characters are not representative of phylogenetic history of Odontasteridae. We can conclude that species present in high latitudes in the Southern Hemisphere (i.e., Southern Ocean) are the most derived taxa. Additionally, mtDNA data suggest unrecognized lineages of odontasterids are present in high southern latitudes. A new species Odontaster cynthiae sp. nov. is described from the Galapagos Islands.

Appendices

Appendix 1

See Table 3.

Table 3 Matrix of morphological characters

Appendix 2

See Fig. 9.

Fig. 9

Bayesian inference topology for 16S sequence data. Analysis details are provided in text. Number next to node indicates Bayesian posterior probabilities

Appendix 3

See Fig. 10.

Fig. 10

Bayesian inference topology for COI sequence data. Analysis details are provided in text. Number next to node indicates Bayesian posterior probabilities

Appendix 4

See Fig. 11.

Fig. 11

All morphological characters mapped onto Bayesian inference tree. Analysis details are provided in text. Bars indicate where a change has occurred, and squares indicate character reversals or loss of a character. Asterisks indicate character states that were equally parsimonious at a node

Appendix 5. Morphological Character analysis of Odontasteridae

1.:

Recurved spine on oral plates: 0 = absent, 1 = one spine, 2 = two spines

 :

Whether one or two recurved spines were present in the last common ancestor of Odontasteridae cannot be determined here. Hoplaster lacks a recurved spine, which is a lost character. Acodontaster, Eurygonias, Odontaster have one recurved, glassy spine per oral plate; Diplodontias has two recurved, glassy spines per oral plate, while the recurved, glassy spines are missing in Diabocilla and Hoplaster. Number of changes on tree (changes) = 2; Consistency Index (CI) = 1.0

2.:

Abactinal plates: 0 = tabulate, 1 = paxillate, 2 = highly paxillate

 :

Tabulate abactinal plates are inferred as an ancestral character, with a change occurring in Eurygonias hyalacanthus and Odontaster species. A change to highly paxillate occurs in O. validus. Acodontaster has tabulate abactinal plates. Diplodontias has sub-tabulate abactinal plates. Eurygonias has abactinal plates that are paxillar and club-shaped. Hoplaster has abactinal plates that are tabulate. Overall, Odontaster has somewhat paxillate abactinal plates, although some species tend to have a more tabulate look. Changes = 3; CI = 0.67

3.:

Abactinal spines per plate: 0 = (5–10), 1 = (11–15), 2 = (16–20), 3 = (21–25), 4 = (26–30), 5 = (30 and above)

 :

Diplodontias and Eurygonias have the most spines, while a change occurs in Diplodontias singularis from a category 5 to 4. Changes = 10; CI = 0.45

4.:

Abactinal spine: 0 = smooth spines, 1 = rough spines

 :

Whether the last common ancestor of Diplodontias had either smooth or rough abactinal spines cannot be determined. Acodontaster, Eurygonias, Hoplaster, and Odontaster share a common ancestor that likely had rough abactinal spines. Smooth or rough texture of spines on abactinal spines is not genus specific and varies greatly from species to species. Changes = 5; CI = 0.167

5.:

Glassy granules on abactinal plate: 0 = absent, 1 = present

 :

Glassy granules are a derived character present only in Diplodontias miliaris, Diplodontias dilatatus, Hoplaster spinosus, O. aucklandensis, O. australis, O. cynthiae. Changes = 2; CI = 0.5

6.:

Abactinal spine shape: 0 = granular, 1 = short, stout, 2 = short, slender, 3 = clavate, 4 = long, slender, 5 = long, slender prominent spine in middle

 :

Granular abactinal spines are inferred as the most ancestral state. A change occurs in Eurygonias hyalacanthus, which has short, slender spines. A change also occurs at the base of the Odontaster clade to clavate spines. A reversal to granular spines occurs in O. penicillatus. A change occurs in O. validus and O. robustus to long, slender spines. Acodontaster and Diplodontias species all have granular abactinal spines. Diabocilla and Hoplaster species have clavate or club-shaped spines, while Eurygonias has short, slender spines. Odontaster species tend to have a variation of spine shapes. Changes = 7; CI = 0.71

7.:

Papulae on abactinal surface: 0 = restricted to arms and central disk, not found interradially, 1 = absent from disks center and interradial area, 2 = covering entire abactinal surface

 :

Papulae covering the entire abactinal surface are inferred as an ancestral character in Eurygonias hyalacanthus and Diplodontias species. Odontaster and Acodontaster species have papulae restricted to the arms and central disk. A reversal has occurred in Hoplaster kupe, which has papulae covering the entire abactinal surface. Changes = 3; CI = 0.67

8.:

Marginal plate border: 0 = plates form even border with abactinals, 1 = plates form slightly raised border with abactinals, 2 = plates form distinct border with abactinals

 :

The inferred ancestral character is marginal plates that form a slightly raised border with the abactinals, while a change to forming an even border occurs at the base of the Acodontaster and Odontaster clade. A character reversal to a slightly raised border occurs in O. crassus, O. meridionalis, O. pearsei, and O. roseus. Acodontaster hodgsoni has marginal plates that form a distinct border with the abactinal plates. Changes = 4; CI = 0.50

9.:

Grooves between marginal plates: 0 = grooves not distinct, 1 = deep grooves between plates

 :

Diplodontias and Eurygonias hyalacanthus have deep grooves between plates. It is equally parsimonious that either deep grooves or grooves not distinct between marginal plates were present in the last common ancestor of Acodontaster and Odontaster. Odontaster species have deep grooves between marginal plates, while Acodontaster do not. Changes = 4; CI = 0.25

10.:

Marginal plate shape: 0 = wider than long, 1 = square (block-like), 2 = wedge-shaped, 3 = rectangular round

 :

Square-shaped marginal plates are inferred as ancestral, with change occurring in Acodontaster conspicuus and Eurygonias hyalacanthus to rectangular round-shaped plates. Diplodontias miliaris, O. crassus, O. benhami, O. meridionalis, O. pearsei, O. penicillatus, and O. roseus have plates that are wider than long. A reversal occurs in O. validus. Changes = 7; CI = 0.43

11.:

Superomarginal plates: 0 = densely covered in spines of same length, 1 = densely covered in spines getting longer toward the edge of the plate

 :

With the exception of Hoplaster kupe, O. crassus, and O. hispidus, all members of Odontasteridae have superomarginal plates densely covered in spines of the same length. Acodontaster, Diplodontias, Eurygonias species have superomarginal plates densely covered in spines of the same shape. Diabocilla, Hoplaster, and Odontaster species vary between densely covered in spines of the same shape and densely covered in spines getting longer toward the edge of the plate. Changes = 3; CI = 0.33

12.:

Spines on superomarginal plates: 0 = granules, 1 = spinelets

 :

Granules for spines on the superomarginal plates are inferred as the ancestral character state. A change occurs at the base of the Odontaster clade. Reversals occur in Odontaster crassus, O. mediterraneus, and O. penicillatus. Acodontaster, Diplodontias, and Eurygonias have granules for spines on the superomarginal plates. Diabocilla and Hoplaster have spinelets on the superomarginal plates, while Odontaster is varied, with some species having granules and some with spinelets. Changes = 5; CI = 0.20

13.:

Inferomarginal plates: 0 = densely covered in spines of the same length, 1 = densely covered in spines getting longer toward the edge of the plate

 :

With the exception of Hoplaster kupe, O. crassus, and O. hispidus, and O. penicillatus, all members of Odontasteridae have inferomarginal plates densely covered in spines of the same length. Acodontaster, Diplodontias, and Eurygonias have granules for spines on the inferomarginal plates. Diabocilla has spinelets on the superomarginal plates, while Hoplaster and Odontaster are varied, with some species having granules and some with spinelets. Changes = 4; CI = 0.25

14.:

Spines on inferomarginal plates: 0 = same as superomarginal plates, 1 = longer than superomarginal plates, 2 = granules, with one long, prominent spine toward the outside edge of the plate

 :

Diplodontias, Eurygonias hyalacanthus, and Acodontaster have spines on inferomarginal plates that are the same as the superomarginal plates. A change to longer spines occurs in O. meridionalis, O. pearsei, O. penicillatus, and O. roseus. Acodontaster marginatus has one long, prominent spine toward the outside edge of the plate. Most Acodontasterspecies have spines that are the same length as the spines on the superomarginal plates. Changes = 4; CI = 0.50

15.:

Glassy granules on superomarginal plates: 0 = absent, 1 = present, 2 = present only on plates toward the arm tips

 :

The presence of glassy granules on the superomarginal plates is inferred as an ancestral character found in Diplodontias and Eurygonias hyalacanthus. Absence of glassy granules occurs at the base of Acodontaster and Odontaster, with changes in O. benhami, O. crassus and O. mediterraneus. Odontaster hispidus has glassy granules present only on the plates toward the arm tips. Changes = 5; CI = 0.40

16.:

Glassy granules on inferomarginal plates: 0 = absent, 1 = present, 2 = present only on plates toward the arm tips

 :

The ancestral state of the glassy granules on the inferomarginal plates cannot be determined. Glassy granules are present in hyalacanthus, Diplodontias dilatatus, D. miliaris, Odontaster benhami, O. crassus, and O. mediterraneus. Odontaster hispidus has glassy granules, but only on the plates toward the arm tips. Changes = 6; CI = 0.33

17.:

Number of chevrons on actinal surface: 0 = 3, 1 = 4, 2 = 5, 3 = 6, 4 = 7

 :

The number of chevrons present on the actinal surface is quite variable across and within all genera (character not mapped on Fig. 8)

18.:

Spines per plate on actinal surface: 0 = (4–9), 1 = (10–15), 2 = (16–20), 3 = (8–10 with one prominent longer spine)

 :

The number of spines per plate on the actinal surface is varied across genera and species within genera. Sixteen to twenty spines per plate on the actinal surface was inferred as the ancestral state. Changes occur at the base of the Diplodontias miliaris and D. dilatatus clade and several times throughout Acodontaster and Odontaster clades. Changes = 10; CI = 0.10

19.:

Glassy granules on actinal surface: 0 = absent, 1 = present

 :

Acodontaster, Diabocilla, Diplodontias, Eurygonias, and Hoplaster are all lacking in glassy granules on the actinal surface. Only two members of Odontaster have glassy granules present on the actinal surface. Changes = 1; CI = 1.0

20.:

Number of furrow spines: 0 = (1–2), 1 = (2–3), 2 = (3–4), 3 = (4–5)

 :

The number of furrow spines is varied across and within taxa. The majority of taxa have 2–3 furrow spines. Changes = 9; CI = 0.33

21.:

Furrow spine shape: 0 = smooth, cylindrical, 1 = smooth, pointy, 2 = rough, cylindrical, 3 = rough, pointy

 :

Diplodontias species and E. hyalacanthus have smooth, cylindrical furrow spines. A change to smooth, pointy spines occurs at the base of the Acodontaster and Odontaster clade. Further changes occur within the Odontaster and Acodontaster clades. Character reversal to smooth, cylindrical furrow spines occurs in O. benhami, O. hispidus, and O. penicillatus. Changes = 14; CI = 0.21

22.:

Adambulacral plate shape: 0 = rectangle, 1 = square

 :

The ancestral character state is inferred as rectangular adambulacral plates. Character state changes occur in lineages leading to Acodontaster hodgsoni, A. marginatus, Hoplaster kupe, Odontaster penicillatus, and O. robustus. Changes = 5; CI = 0.20

23.:

Pedicellariae: 0 = absent, 1 = present

 :

All Acodontaster, except A. capitatus, have pedicellariae. Diabocilla, Hoplaster, and Diplodontias (except D. singularis) are lacking pedicellariae. Eurygonias and several members of Odontaster have pedicellariae. Type and appearance of pedicellariae are variable. Changes = 3; CI = 0.33

24.:

Body shape outline: 0 = pentagonal, 1 = sub-pentagonal, 2 = pentagonal-stellate, 3 = sub-stellate, 4 = stellate

 :

Determination of the body shape outline in the last common ancestor of Odontasteridae is not possible. Changes = 12; CI = 0.33

25.:

Interradial arc: 0 = rounded, 1 = sub-linear, 2 = linear

 :

A rounded interradial arc is the inferred ancestral character state. All Acodontaster and the majority of Diplodontias species have rounded interradial arcs. Diabocilla and Hoplaster have sub-linear interradial arcs, while Odontaster have either rounded or sub-linear interradial arcs. Eurygonias has a completely linear interradial arc. Changes = 6; CI = 0.33

26.:

Arm length: 0 = short, 1 = medium, 2 = elongate

 :

Acodontaster have elongate arms. Diabocilla has medium length arms, and Diplodontias, Hoplaster, and Odontaster have a variety of arm length, while Eurygonias have very short arms. Changes = 12; CI = 0.17

27.:

Number of apical spines per oral plate: 0 = 2, 1 = 3, 2 = 4, 3 = 5, 4 = 6

 :

The majority of taxa have four apical spines per oral plate. Changes occur at terminal nodes within Acodontaster and Diplodontias. Several changes occur throughout the Odontaster clade (character not mapped)

28.:

Number of suboral spines per oral plate: 0 = 2, 1 = 3, 2 = 4, 3 = 5, 4 = 6+

 :

The character state of last common ancestor of Odontasteridae is equivocal with either two or three suboral spines per oral plate. The number of suboral spines per oral plate is variable across and within genera (character not mapped).

29.:

Number of marginal spines per oral plate: 0 = (2–3), 1 = (3–4), 2 = (4–5), 3 = (5–6), 4 = (6–7)

The number of marginal spines per oral plate is variable across and within genera (character not mapped)