Temnothorax salvini clade

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based on Prebus 2017, 2020, 2021

Introduction

Prebus (2017) provided evidence for the Nearctic origin of the crown Temnothorax, followed by a rapid radiation across the majority of the present-day range. This initial radiation resolved into seven large clades, including several lineages that dispersed to the Neotropics soon after the origin of the crown group. Among these early-arriving Neotropical lineages is the morphologically heterogenous salvini clade. See Prebus, 2017 and the Temnothorax clades webpage for more information about the resolution of the Temnothorax into these seven clades. Subsequent studies (Prebus 2020, 2021) have produced a better understanding the evolutionary development and taxonomy of the diverse salvini clade.

Diagnosis

As per Prebus, 2021: based on the worker caste, the T. salvini clade lack a singular diagnostic feature, but can be diagnosed with the following combination of characters:

  1. Antennae composed of 12 antennomeres.
  2. Postpetiole moderately to very broad: 1.4 to 3 times as broad as the caudal cylinder in dorsal view (PWI 140-300); if less than 1.5 times, then antennal scapes are moderately short, failing to reach the posterior margin of the head by the maximum width of the antennal scape or less, and dorsum of propodeum lacks standing setae.
  3. Anterodorsal region of petiole with or without tubercles that are united by a transverse carina; if tubercles present, then median lobe of clypeus bearing many (> 3) fine carinae, femora incrassate (FI> 250), or, if femora not incrassate, then dorsum of propodeum lacks standing setae.
  4. Propodeum bearing teeth or spines; or, if propodeum is unarmed, then propodeum is strongly depressed below the level of the evenly convex promesonotum.
  5. Legs usually without long tapering setae, but if present, then medial lobe of clypeus bearing many (> 3) longitudinal carinae, or propodeum is strongly depressed below the level of the evenly convex promesonotum.

The Macromischa syndrome

The synonymized genus Macromischa is one of more than a dozen previously proposed genera entirely comprised of Temnothorax species. The name Macromischa was broadly applied to both Baltic amber fossils and extant Neotropical species of Temnothorax bearing a peculiar morphological syndrome, e.g., Temnothorax purpuratus, Temnothorax gundlachi, Temnothorax allardycei, Temnothorax nigricans, Temnothorax poeyi and Temnothorax squamifer. The primary diagnostic features of this syndrome are a thin, elongate petiole combined with a broad, campaniform post-petiole in dorsal view and a dorsally contiguous, often rounded, mesosoma in profile. Not always present, but also associated with this syndrome, are enlarged, spindle-shaped middle and hind femora and an iridescently colored integument. Baroni Urbani (1978) found Macromischa was putatively polyphyletic, and this was subsequently more definitively affirmed by Prebus (2017). He showed that several clades of Temnothorax dispersed to the Neotropics soon after the origin of the crown group, and that several of these Neotropical lineages converged upon at least part of the Macromischa syndrome. A challenging but potentially fruitful line of research would be to discover and understand the drivers of the diverse and species-rich radiation of Temnothorax in the Greater Antilles, and why independent clades have in part shown a convergence on the Macromischa syndrome.

Identification

Key to New World Temnothorax clades

Key to Temnothorax salvini clade workers

Species Groups

As per Prebus, 2021: the clade is organized, using a combination of molecular and morphology data (Prebus 2017, 2020, and unpublished), into species groups that are used here to correspond to morphologically-diagnosable groups of species.

acuminatus group

This group is composed of two previously undescribed species, T. acuminatus and T. tuxtlanus. They occur in the southern Mexican mountains of Los Tuxtlas and the Sierra Madre de Chiapas at mid-to-high elevations. These species are united by the lack of setae on the dorsum of the propodeum, reduced subpetiolar tooth, moderately impressed metanotal groove, posterodorsally directed propodeal spines, and dark coloration. The two species of this group have been collected from bark crevices, under epiphyte mats on treefalls, and sifted leaf litter.

Species of the acuminatus group may be confused with Temnothorax acutispinosus, which has an overlapping distribution, similar habitus, and lack of setae on the propodeum. Temnothorax acutispinosus can be distinguished from the acuminatus group by the larger subpetiolar tooth and dorsally directed propodeal spines. The two species of the acuminatus group are sister to the remainder of the salvini clade (Prebus, in prep.).

acuminatus group species

acutispinosus group

This group is monotypic, with the nominal T. acutispinosus being the only member. It is morphologically similar to the members of the acuminatus group, with which it overlaps geographically, but differs from them by the larger subpetiolar tooth and dorsally directed propodeal spines. However, T. acutispinosus is apparently more closely related to the members of the rugosus and annexus groups (Prebus, in prep.).

altinodus group

This group is monotypic, with the nominal T. altinodus being the only member. It is morphologically similar to the members of the acuminatus and acutispinosus groups, sharing a lack of setae on the propodeal dorsum. It can be distinguished from these groups by the larger subpetiolar tooth (small in the acuminatus group) and the incrassate femora (not incrassate in the acuminatus and acutispinosus groups). Known from a single collection in the mid elevations of Honduras, this species is apparently sister to the fuscatus and pergandei groups (Prebus, in prep.).

annexus group

A relatively small group (5 species) with a range spanning the low-to-mid elevations of the American southwest to central Mexico. Although collections for many of these species are scant, all nest collections so far have been from habitats associated with vegetation, either from epiphytes (T. annexus) or from hollow branches and stems on live vegetation (T. arbustus, T. balnearius, T. obtusigaster, and T. quercicola). As collections accumulate, this may prove to be the rule.

Temnothorax quercicola has a long history of being conflated with Temnothorax silvestrii, to the extent that Creighton (1953) described the male and gyne of T. quercicola as T. silvestrii. The two species are superficially similar, but T. silvestrii belongs to another clade entirely (the sallei clade), in yet another example of convergent evolution in Temnothorax. These species are large, and typically have an emarginate clypeus, short petiolar peduncle, subquadrate petiolar node, and incrassate femora.

annexus group species

augusti group

The range of the four augusti group species spans the low-to-mid elevations of central Mexico to Central America. Although little is known about the biology of the members of this group, the nominal T. augusti was collected from epiphytes, and T. leucacanthoides was collected from a dead stalk of Asteraceae; nesting in vegetation may prove to be the rule for this group as more collections are made.

Members of this group may be confused with Temnothorax casanovai or Temnothorax tenuisculptus. They may be separated from these by the petiolar node that overhangs the caudal cylinder (perpendicular in T. tenuisculptus) and the faintly areolate first gastral tergite (strongly areolate in T. casanovai).

augusti group species

casanovai group

This group is monotypic, with the nominal T. casanovai being the only member. With only a couple of collections from mid elevation southern Mexico, this species is morphologically similar to the members of the augusti group, in that it has a subquadrate petiolar node that overhangs the caudal cylinder. It can be separated from them by the overall larger size of T. casanovai, the shorter propodeal spines, smaller metapleural gland bulla, and longer antennal scapes. Despite the morphological similarities to the augusti group, this species is more closely related to Temnothorax subditivus (Prebus, in prep.).

fuscatus group

With four species, the fuscatus group is another small group with a range spanning the mid-to-high elevations of central Mexico to southern Central America. All nest collections of fuscatus group species have been from arboreal habitats, either nesting in vegetation (alive or dead) on live trees or in epiphytes. The low, long petiolar node distinguishes this group from nearly everything else in the salvini clade. Apparently, the fuscatus group is sister to the ground-nesting pergandei group (Prebus, in prep.).

fuscatus group species

goniops group

The five species of the goniops group occur in the low-to-mid elevations of Central America and the Yucatán Peninsula of Mexico. Nest collections of the members of this group have been rare and restricted to those made from orchids in quarantine at United States ports of entry. Other collections have been made from leaf litter extractions.

The generalized habitus of the members of this group make them easy to confuse with others in the salvini clade. They can be separated from other species with conservative morphology such as the acuminatus group, Temnothorax acutispinosus, and Temnothorax altinodus by the presence of erect setae on the dorsum of the propodeum (absent in the preceding species), from Temnothorax subditivus by the petiolar node (squamiform in T. subditivus), and from members of the pulchellus group by geography (the pulchellus group spans the islands of the Caribbean and southern Florida).

goniops group species

misomoschus group

This group is monotypic, with the nominal T. misomoschus being the only member. With its depressed propodeum, strongly curved propodeal spines, and nearly complete lack of standing setae, this species is distinctive in the salvini clade, not to mention the genus as a whole. Collected from only a couple of geographically disparate collections (southern Texas and Nicaragua), this species apparently has a large range, but we still know little about its biology. It is sister to the goniops group (Prebus, in prep.).

pastinifer group

The five species of the pastinifer are found in the low elevations of the Bahamas and Cuba. The group is likely composed of littoral specialists, as it has only been collected from low-lying habitats near the sea. Most nest collections have been taken from wood or woody fruits lying on the ground.

These distinctive species have extremely arched mesosomata, broad postpetioles, and incrassate femora, and so are prime examples of the Macromischa syndrome (the characters of this syndrome are detailed in the Diagnostic section above). Members of the pastinifer group may be confused with Temnothorax subditivus, members of the pulchellus group, or morphologically convergent members of the sallei clade. Because of multiple character overlaps between these groups, the key to New World Temnothorax clades and key to T. salvini-clade workers, along with the ʻsimilar species' sections of each groups noted here, should be used to determine species group membership. The nominal T. pastinifer and T. rutabulafer have historically been conflated as a single species, probably due to a mixed pin prepared by W.M. Mann.

pastinifer group species

pergandei group

This group is composed of two species, T. pergandei and T. bison, which are found at all elevations from eastern North America to Central America. For much of its history, the nominal species of this group was placed in its own subgenus (Dichothorax). All nest collections have been made from soil or dead vegetation on the ground thus this appears to be a primarily terrestrial group.

United by a strongly depressed propodeum, long setae on all surfaces of the body, and reduced or absent propodeal spines, the members of the pergandei group are unlikely to be confused with any co-occurring Temnothorax species. They do interestingly appear to be morphologically convergent with some species of the Mediterranean region of Europe.

pergandei group species

pilicornis group

This group is monotypic, with the nominal T. pilicornis being the only member. Known only from coastal habitats and offshore islands of Baja California, this species has a generalized Temnothorax habitus, save for the extremely broad postpetiole. It can be separated from most similar appearing species be the combination of the broad postpetiole and erect setae on the antennal scapes.

pulchellus group

With fifteen species, the pulchellus group is the largest in the salvini clade. Primarily inhabiting low elevations on Caribbean islands and southern Florida, the group as a whole has a peculiar bimodal elevational distribution. Two species inhabit some of the highest points on the island of Hispaniola, but as of yet there are no mid-elevation collections for any species in the group. Nest collections, while rare, suggest nesting habits similar to the pastinifer group, i.e., within dead wood and vegetation on or near the ground, often in leaf litter.

The general habitus of the members of the pulchellus group is another example of the Macromischa syndrome (the characters of this syndrome are detailed in the Diagnostic section above), with most species having extremely arched mesosomata, often with enlarged femora, and always with broad postpetioles. These characters broadly overlap with the pastinifer group, Temnothorax subditivus, and some members of the sallei clade (e.g., the sallei and iris subclades sensu Prebus (2017)). Use the key to New World Temnothorax clades and key to T. salvini-clade workers, along with the ʻsimilar species' sections of each of the groups noted here, to find specific distinguishing characters.

pulchellus group species

rugosus group

This group is composed of two species, T. parralensis and T. rugosus, which are found at mid-to-high elevations in the southern United States to central Mexico. Members of this group have been collected from dead branches on live trees, mostly Quercus spp. The species of the rugosus group, with their arboreal nests, large size, coarse sculpturing, and somewhat incrassate femora, are very similar in habitus to the annexus group, but differ from them by their relatively short propodeal spines and shape of their petiolar nodes (cuneiform to truncate).

rugosus group species

salvini group

With ten species, the salvini group is the second largest in the salvini clade. Up until a recent species delimitation study (Prebus, 2020), this group was thought to contain two species, T. aztecus and T. salvini, but upon including specimens from across its considerable geographic range and morphological variability, this group was found to contain an additional seven species. Following publication of this study, another species was discovered that had been overlooked in collections (T. terraztecus). The members of the salvini group inhabit all elevations throughout their range in southern Mexico and Central America, but individual species appear to have an affinity for nearly discrete elevational ranges when their geographic ranges overlap with other members of the salvini group. Prebus, 2020 illuminated some of the biogeographic history of the salvini group as well: it was inferred to have arisen in the northern part of its current range in habitats associated with contemporary mid-to-high elevations in the Miocene, approximately 13 Ma. Subsequently, the salvini group expanded into the southern Central American Cordilleras at the Miocene-Pliocene transition, coinciding with mountain building in that region 8-5 Ma, where today it is represented by T. salvini and T. longicaulis, Additionally, the salvini group expanded into low elevation habitats during the same transition period, with the widespread T. aztecus being the only member of the group inhabiting these habitats today. The nesting habits of the species of the salvini group, where they are known, are almost exclusively arboreal, nesting in vines, under epiphytes, or in dead vegetation suspended in the canopy. The one exception may be T. terraztecus, which has only been collected from leaf litter extractions from a couple of localities.

While the species within the salvini group can be difficult to tease apart morphologically, as a group they are quite distinctive, with long, tapering setae on all surfaces of the body, flat to slightly sinuate mesosomata in profile, and strongly sculptured head and mesosomata.

salvini group species

subditivus group

This group is composed of two species, T. politus and T. subditivus. These species together have a vast range from the southern United States to northern South America, and can be found at all elevations. Nests are typically located in dead vegetation, under bark, or in the leaf litter. Finer details of the biology of this group remain unknown. All nest collections so far have been monogynous.

The morphology of T. subditivus is extremely variable across its range and it may be a species-complex (more sampling and further study is needed). As a species group, T. politus is easy to distinguish from other Nearctic Temnothorax, but the morphological characteristics and range of T. subditivus overlap broadly with the pulchellus group, the pastinifer group, and members of the sallei clade with characters of the Macromischa syndrome (the characters of this syndrome are detailed in the Diagnostic section above). The key to New World Temnothorax clades and key to T. salvini-clade workers, along with the ʻsimilar species' sections of each of the groups noted here, provide distinguishing characters that separate the two species of this group from lookalikes.

subditivus group species

tenuisculptus group

This group is monotypic, with the nominal T. tenuisculptus being the only member. The range of this species as we currently understand it is small, restricted to the low elevations of the Southern Sierra Madre and Los Tuxtlas in southern Mexico. It is morphologically similar to the members of the augusti group and is contained within its geographical range. Unlike the members of the augusti group, the petiolar node of T. tenuisculptus is erect, not leaning posteriorly. This species is sister to the annexus group (Prebus, in prep.).

terrigena group

This group is monotypic, with the nominal T. terrigena being the only member. The range of T. terrigena is small, restricted to the low elevations of the southern United States and northern Mexico. Apparently, this species is ground nesting. The generalized habitus of this ant has historically led to confusion about its relationships, but the moderately arched mesosoma dorsum and broad postpetiole are telltale signs of its membership in the salvini clade. Temnothorax terrigena may be confused with members of the andrei and sallei clades, and other members of the salvini clade (see the T. terrigena identification section for more details).

Other Resources

References

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