Leptomyrmex relictus Boudinot, Probst, Brandão, Feitosas &amp; Ward, 2016, sp.n.
Creators: name: Brendone Boudinot
name: Rodolfos Probst
name: Brandão, Carlos Roberto F.
name: Feitosas, Rodrigo
name: Ward, Philip S.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Formicidae
Leptomyrmex
Leptomyrmex relictus

description: <i>Leptomyrmex relictus</i> sp.n. http://zoobank.org/urn:lsid:zoobank.org:act: 936 F 5440 - 9 B 94 - 43 C 0-95 ED- 2099 FD 380471 (Figs. 1–5, Figures S 1, S 2) <i>Type material. Holotype worker. BRAZIL, Goiás: Niquelândia, Serra da Mesa, 14 &amp;compfn; 20 ′ 39.5 ′′S, 48 &amp;compfn; 10 ′ 21.1 ′′W, 16.xi. 2013, cerrado, inside nest of <i>Cornitermes silvestrii</i> (<i>D. E. Oliveira, R. G. Santos &amp; T. Carrijo</i>) (sample code DEO 2013 -030; specimen code CASENT0106501) [MZSP].</i> <i>Paratype workers</i> (w) <i>and males</i> (m). Same data and colony as holotype; sample code R06 [1 w MZSP, 1 w (CASENT0730400) 1 m UCDC]; sample code TC08 [1 w DZUP, 1 w MZSP]; sample code DEO 2013 -030 [1 w LACM, 1 m MZSP]. Additional material examined (nontype): 12 w, 6 m, 3 larvae, and 2 pupae from 6 localities in Goiás and Tocantins, Brazil (Fig. 2). <i>Diagnosis.</i> With diagnostic characters of genus from Shattuck (1992), notably with medial hypostomal notch (synapomorphy of genus) and lacking pterostigmal appendage in male (synapomorphy of macro- <i>Leptomyrmex</i>). Distinguished from all <i>Leptomyrmex</i> by the following characters: (i) short, thick, erect setae present on the head capsule, mesosoma (legs included) and metasoma (Figs 1 A, 3 A, B); (ii) clypeal setae comparatively more numerous (Figs 1 E, 3 B); (iii) anterior clypeal margin strongly convex (Figs 1 E, 3 B); (iv) lateral hypostoma weakly flanged; (v) worker with convexity subtending subapical mandibular tooth (Fig. 1 E); (vi) worker petiole lateromedially narrow; (vii) worker gaster strongly lateromedially compressed; (viii) male scape elongate (SI 1.26–1.40 versus 0.19–1.05 in other <i>Leptomyrmex</i>); (ix) male wing with five closed cells (costal, basal, subbasal, submarginal 1, marginal 1) (Fig. 5 E); (x) male petiole dorsal margin concave (Fig. 3 A); (xi) male petiolar spiracles situated on tubercles (Fig. 3 A); (xii) several features of male genitalia (Fig. 3 C–K; see Appendix S 2 for description). Characters 1 –5, 9– 11 and those of 12 are unique in the genus. <i>Biology.</i> Although males of <i>L. relictus</i> have been collected as far back as 1956 – remaining unidentified for over half a century – workers were only recently discovered in 2013 from nest samples of <i>Cornitermes silvestrii</i> Emerson and in 2012 from epigaeic and arboreal pitfall traps in typical cerrado (Brazilian savannah) habitat. It is unknown whether workers are nocturnal or diurnal, but hypothetical nocturnal habits and/or their <i>Camponotus</i> -like habitus may account for the low encounter rate of this species. It is interesting to note that at least three of the specimens were captured in arboreal pitfall traps, suggesting that workers may forage both on the soil and in the vegetation strata. The collection of workers (Fig. 1 A, E) and brood (Figure S 1) inside termitaria suggests that <i>L. relictus</i> may live in association with <i>Cornitermes silvestrii.</i> One termite nest measuring 1.30 m wide and about 40–50 cm tall inhabited by <i>L. relictus</i> was found in northeast Goiás state under a tree, and was also occupied by another ant species, <i>Camponotus blandus</i> (Smith, F.), which is known to be a facultative termite inquiline (Gallego-Ropero &amp; Feitosa, 2014). The other termite nest with <i>L. relictus</i> specimens was found in southeast Tocantins state, along a trail edge. Unfortunately, no data are available on how the <i>Leptomyrmex</i> occupy the termitaria or if they were sharing galleries with the termites. A potential association with <i>C. silvestrii</i> is compelling as the termitaria of <i>C. silvestrii</i> are large, environmentally-stable clay mounds and may house several other ant and termite species (see Appendix S 2). In addition to describing and comparing the sociometric and sociogenic patterns (Tschinkel, 1991, 2011) of <i>L. relictus</i> with the Australian species, future studies should test the association of the species with <i>C. silvestrii</i>. <i>Phylogeny.</i> Phylogenetic analyses of the 10 -gene dolichoderine data matrix yielded results congruent with those of Ward <i>et al.</i> (2010) (Fig. 4). In particular, we consistently recovered all four dolichoderine tribes, with Tapinomini as sister to all other Dolichoderinae. <i>Leptomyrmex relictus</i> is positioned as sister to the six Australian <i>Leptomyrmex</i> with strong support: Bayesian posterior probability (PP) of 0.96, and ML bootstrap support (MLBS) of 93 %. There is maximum support (PP 1.00, MLBS 100 %) for the Australian <i>Leptomyrmex</i> and for the micro- and macro- clades within it. Our results differ from those of Lucky (2011) for the internal topology of <i>Leptomyrmex</i> in that, with our sampling, <i>L. unicolor</i> is sister to <i>L. erythrocephalus</i>, rather than <i>L. geniculatus</i> + <i>L. rufithorax</i>. A sister-group relationship between <i>Leptomyrmex</i> and the (<i>Forelius</i> Emery + <i>Dorymyrmex</i> Mayr) clade is also sustained (PP 1.00, MLBS 74 %). Finally this larger clade of (<i>Leptomyrmex</i> + (<i>Forelius</i> + <i>Dorymyrmex</i>)) is sister to all other Leptomyrmecini, as in Ward <i>et al</i>. (2010). Notably, <i>L. relictus</i> is a long-branched taxon; because its divergence from the most recent common ancestor of the crown <i>Leptomyrmex</i>, it is apparent that <i>L. relictus</i> has undergone considerable morphological (especially genitalic) and molecular evolution. <i>Divergence dating.</i> Two alternate analyses were run treating † <i>Chronomyrmex</i> as a stem dolichoderine, reflecting uncertainty of stem or crown placement of † <i>L. neotropicus</i> with respect to extant <i>Leptomyrmex</i>. Dating results obtained were robust to alternate placements of † <i>L. neotropicus</i>. The chronogram from the stem <i>Leptomyrmex</i> treatment is presented in Fig. 5. Mean ages between the two treatments for the clades listed in Table S 3 differed by an average of 0.21 Ma, and 95 % highest probability densities (hpd) differed by an average of 0.26 Ma at the older and 0.53 Ma at the younger ends, respectively. These findings are in accord with results of Ward <i>et al.</i> (2010) and Lucky (2011) (Table S 3), although less so with the latter which incorporated fewer outgroups and loci. Only the dolichoderomorph crown age differed notably from Ward <i>et al.</i> (2010), being 11 Ma younger. This difference is attributable to the modified dolichoderomorph root node calibration used herein which is a diffuse normal distribution, not restricting the minimum age of the node to 100 Ma with the unplaceable yet putative aneuretine fossil † <i>Burmomyrma</i>. <i>Biogeographical history.</i> The LAGRANGE analysis was run with a single outgroup taxon (<i>Aneuretus simoni</i> Emery) (Fig. 5), and all results are presented in Table S 4. A Neotropical origin was recovered with high support (relative probabilities <b>&gt;</b> 0.80) for the Leptomyrmecini, the <i>Leptomyrmex</i> + (<i>Dorymyrmex</i> + <i>Forelius</i>) clade and <i>Leptomyrmex</i> (Fig. 5 A). The crown ages of <i>Leptomyrmex</i> and the Australasian clade are estimated to be 46 Ma (95 % hpd 53 – 37 Ma) and 28 Ma (95 % hpd 40 to 18 Ma), respectively (Table S 3, calibration 2). We therefore infer dispersal to Australia between those two time periods. This range expansion probably happened before the breakup of the Antarctic land bridge, estimated to have occurred about 35 Ma for Australia and Antarctica, and about 30 to 28 Ma for Antarctica and South America (Lawver <i>et al.</i>, 1992; Sanmartín &amp; Ronquist, 2004). Another notable result is an inferred Neotropical origin for the Dolichoderini (comprising solely <i>Dolichoderus</i> Lund) (Fig. 5 A). Only four nodes had relative probabilities <b>&lt;</b> 0.33 for inferred ancestral ranges: the crown and root Dolichoderinae, the BDL (Bothriomyrmecini + Dolichoderini + Leptomyrmecini) clade, and the Bothriomyrmecini. All other relative probabilities were <b>&gt;</b> 0.66, except the <i>Liometopum</i> + <i>Aptinoma</i> Fisher + <i>Tapinoma</i> Foerster clade, which had a relative probability between 0.33 and 0.66. Further sampling within the Bothriomyrmecini is expected to increase the relative probabilities of inferred ancestral ranges for the tribe as well as the BDL clade. <i>Results and evaluation of fossil record.</i> Dlussky <i>et al.</i> (2014) claimed that † <i>Usomyrma</i>, † <i>Leptomyrmula</i> and <i>Leptomyrmex</i> form a natural group based on the putatively synapomorphic ‘reduction of the central vein sections and cells.’ This is refuted by the retention of complete wing venation in the species of micro- <i>Leptomyrmex</i>, which is nested well within the genus. Moreover, the venation reduction patterns of † <i>Usomyrma</i>, <i>Dorymyrmex</i> + <i>Forelius</i> and <i>Leptomyrmex</i> are not homologous. † <i>Usomyrma</i> has lost Rs + M and Mf 2-3; the former is autapomorphic and the latter has occurred at least five times in the Dolichoderinae (Fig. 5). At least two reductions have occurred in <i>Leptomyrmex</i> (Fig. 5) as the micro- clade retains complete wing venation, whereas <i>L. relictus</i>, the macro- <i>Leptomyrmex</i> and † <i>L. neotropicus</i> have differing reduction patterns. <i>Leptomyrmex relictus</i> has lost 1 m-cu and Mf 2-3, † <i>L. neotropicus</i> has lost Rsf 2 +, Mf 2 + m, 2 rs-m, 1 m-cu and 2 r-rs, whereas macro- <i>Leptomyrmex</i> have lost Mf 2 -3, 2r-rs (variable) and 1 m-cu, and retained Rs + M, Rsf 2 + and Mf 4 +. Other characters claimed by Dlussky <i>et al.</i> (2014) to support a relationship between † <i>Usomyrma</i> and † <i>Leptomyrmex</i> are, by their explicit statement, either plesiomorphic or autapomorphic; these are thus uninformative of relationships by definition. Furthermore, based on examination of a paratype male, † <i>Usomyrma</i> lacks a newly discovered genitalic synapomorphy of the Leptomyrmecini: a dorsal sclerotic bridge between the penisvalvar bases. The sclerotic bridge is anteroposteriorly broad and fused with the basimeres in <i>L. relictus</i> (Fig. 2 C, F), and is narrowed anteroposteriorly in the Australasian clade. The strap- or thread-like condition of the bridge in the Australasian clade is a synapomorphy, whereas fusion of the bridge to the basimeres in <i>L. relictus</i> is autapomorphic. Regarding † <i>Leptomyrmula</i> specifically, the only known specimen may be lost (G.M. Bargossi, University of Bologna, Italy, personal communication), but it has fortunately been illustrated (Emery, 1891) (reproduced in Fig. 5 H). The pattern of vein abscissa loss is most similar between † <i>Leptomyrmula</i> and the macro- clade (Fig. 5 F), with the venation being clearly different from the micro- <i>Leptomyrmex</i> (Fig. 5 A) and <i>L. relictus</i> (Fig. 5 E), which have complete or relatively complete wing venation, respectively. Homology of the loss pattern between † <i>Leptomyrmula</i> and the macro- <i>Leptomyrmex</i> is unlikely, however, given the distinctions of the venational patterns. Forewing characters of † <i>Leptomyrmula</i> differ as follows from the macro- <i>Leptomyrmex</i> clade: costal cell broad and short (vs. absent, with secondary sclerotization); free R lacking along the anterior wing margin (vs. continuing almost to wing apex); pterostigmal appendage absent (vs. present); 2 rs-m + Mf 4 + absent (vs. usually present); basal cell narrow and Mf 1 subparallel to Sc + R + Rs (vs. broad, Mf 1 and Sc + R + Rs clearly converging); free Cu short and diverging from M + Cu in the basal third of the wing (vs. about midlength); and anal vein elongated after crossvein cu-a (vs. anal vein strongly reduced or absent). Moreover, the somatic morphology of † <i>Leptomyrmula</i> is considerably divergent, including the following differences: head capsule dorsoventrally compressed; compound eyes small and anteriorly-situated; mandibles small; flagellomeres short; pronotum dorsoventrally tall; mesonotum flat; and limbs short (metatibia not exceeding metasomal apex). Neither † <i>Leptomyrmula</i> nor † <i>Usomyrma</i> have the key macro- <i>Leptomyrmex</i> clade forewing synapomorphies of the pterostigmal appendage (Lucky &amp; Ward, 2010) and the absent costal vein with secondary sclerotization. We therefore consider † <i>Leptomyrmula</i> and † <i>Usomyrma incertae sedis</i> in the Dolichoderinae. The placement of † <i>Leptomyrmula</i> in the Dolichoderinae itself could be questioned because the genitalia, as illustrated in Emery (1891), do not conclusively demonstrate a synapomorphic condition of dolichoderine genitalia: enlarged basimere and reduced telomere (Yoshimura &amp; Fisher, 2011; Boudinot, 2015). Study of worker and male † <i>L. neotropicus</i> specimens revealed presence of the hypostomal notch, a synapomorphy of the genus almost completely unique in the Dolichoderinae, except for the enigmatic leptomyrmecine <i>Anillidris</i> Santschi (B.E. Boudinot, personal observation), confirming placement of the fossil within the genus. Presence of the notch could not be evaluated in either † <i>Leptomyrmula</i> or † <i>Usomyrma</i>; the ventral head surface of the paratype † <i>Usomyrma</i> examined is obscured by a fracture within the amber. It is plausible that † <i>L. neotropicus</i> is more closely related to <i>L. relictus</i> than to the Australasian clade based on genitalic characters, although the placement of the Dominican amber fossil should be tested in a ‘total-evidence’ framework (Ronquist <i>et al.</i>, 2012 b).
description: Published as part of <i>Brendone Boudinot, Rodolfos Probst, Carlos Roberto F. Brandão, Rodrigo Feitosas &amp; Philip S. Ward, 2016, Out of the Neotropics: newly discovered relictual species sheds light on the biogeographical history of spider ants (Leptomyrmex, Dolichoderinae, Formicidae), pp. 658-671 in Systematic Entomology 41</i> on pages 663-667, DOI: 10.1111/syen.12181, http://zenodo.org/record/270273
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