Introduction

The Malagasy region, i.e., Madagascar and the surrounding smaller islands, harbors unique fauna. Madagascar’s fauna is taxonomically imbalanced (Samonds et al., 2013). Many lineages of its extant terrestrial and freshwater assemblages can be characterized by high levels of species endemism (Goodman & Benstead, 2005). Within some other clades, Madagascar’s fauna is species-poor. This is true for ants as well, with the exception of some hyperdiverse genera, e.g., Tetramorium (Hita-Garcia & Fisher, 2014), Camponotus (Rakotonirina et al., 2016; Rasoamanana et al., 2017), and Pheidole (Salata & Fisher, 2021). Other genera, such as the genus Ponera, are represented by only a few species in the region. The genus Ponera, encompassing tiny, endogeic predator ants, is primarily distributed in the Indomalaya and Australasia regions, with a few additional Holarctic species (Leong et al., 2019; Taylor, 1967; Wilson, 1957) and currently contains 60 extant and five fossil species worldwide (https://www.antcat.org/). The taxonomy of the handful of Ponera species in the Malagasy region has never constituted the basis of focused research before.

We, for the first time, revise the Malagasy Ponera species via an integrated taxonomic protocol incorporating morphometrics, morphology, and DNA sequence data. Quantitative analyses of continuous morphometric traits were performed via NC-PART clustering as described by Csősz and Fisher (2016ab). The clusters returned by this protocol are considered species unless this hypothesis conflicts with other biological information. Species boundaries and reliability of morphological clusters were tested via confirmatory Linear Discriminant Analysis (LDA), cross-validation (LOOCV), subjective evaluation of qualitative morphological characteristics, and analyses of a mitochondrial COI gene fragment. According to the combined application of the analyses, altogether, three species are inferred, Ponera petila Wilson (1957), P. swezeyi Wheeler (1933), and P. adumbrans Csősz & Fisher sp. n.

Two of the three known Malagasy Ponera species, P. petila and P. swezeyi, belong to the Indo-Australian Ponera tenuis group; the third species, P. adumbrans sp. n., is morphologically similar to the Papua New Guinean P. clavicornis (Emery, 1900), that further strengthens the Indo-Australian connection hypothesis. Beyond Ponera, five other Malagasy ant genera, Adelomyrmex, Aphaenogaster, Chrysapace, Eurhopalothrix, and Vollenhovia, exhibit this biogeographic pattern, i.e., are not present in Africa but are distributed in India or the Indo-Australian regions (Fisher & Bolton, 2016).

Madagascar’s extant biodiversity is predominantly explained by colonization events from the African continent across the Mozambique channel via rafting once lower sea levels allowed for the journey in the Cenozoic era (Ali & Huber, 2010; Godfrey et al., 2020; Masters et al., 2020). However, the occurrence of Malagasy Ponera species raises issues about the colonization route of the Malagasy Ponera, because (i) there are no known native extant or extinct Ponera species known from the Afrotropical continent, and (ii) both the tenuis group and clavicornis group, to which the Malagasy Ponera belong, almost exclusively exhibit an Indo-Australian distribution. Therefore, an Indo-Australian origin of the Malagasy Ponera fauna should be considered.

Material and methods

Ant samples used in this study comply with the regulations for export and exchange of research samples outlined in the Convention on Biological Diversity and the Convention on International Trade in Endangered Species of Wild Fauna and Flora. For fieldwork conducted in Madagascar, permits to research, collect, and export ants were obtained from the Ministry of Environment and Forest as part of an ongoing collaboration between the California Academy of Sciences and the Ministry of Environment and Forest, Madagascar National Parks and Parc Botanique et Zoologique de Tsimbazaza. Approval Numbers: N° 0142N.EA03.MG02, N° 340N-EV10.MG04, N° 69 du 07.04.06, N° 065N-EA05.MG11, N° 047N-EA05.MG11, N° 083N-A03.MG05, N° 206 MINENVEF.SG.DGEF.DPB.SCBLF, N° 0324N.EA12.MG03, N° 100 l\fEF.SG.DGEF.DADF.SCBF, N° 0379N.EA11.MG02, N° 200N.EA05.MG02. Authorization for export was provided by the Director of Natural Resources. For research in the Seychelles, permits were obtained from the Seychelles Bureau of Standards, Ministry of Environment, and National Park Authority. Material Transfer Agreement was provided by the Seychelles Ministry of Environment.

In the present study, 10 continuous morphometric traits were recorded in 154 worker individuals belonging to 90 nest samples from the Malagasy, Indo-Australian, and Pacific regions.

The material is deposited in the following institutions, abbreviations after Evenhuis (2013): CASC (California Academy of Sciences, San Francisco, California, USA), MCZC (Museum of Comparative Zoology, Cambridge, Massachusetts, USA), MNHN (Muséum National d’Histoire Naturelle), PSWC (Phil S. Ward’s collection, University of California Davis, Davis, California, USA), BPBM (Bernice P. Bishop Museum, Honolulu, Hawaii, USA), HNHM (Hungarian Natural History Museum). Type material and samples that were morphometrically investigated are presented in the “Type material investigated” and “Material examined” sections in the format as follows: CASENT code, collection code, verbatim locality, longitude, latitude, elevation in meters, collector, date (number of individuals measured, abbreviation of depository). Additional information on habitat and microhabitat, whenever available, is given in brackets. For the full list of material, see Supplementary Table S1. All images of specimens are available online on AntWeb (https://www.antweb.org/). Images are linked to their specimens via the unique specimen identifier affixed to each pin CASENT0159966. Digital color montage images were created using a JVC KY-F75 digital camera and Syncroscopy Auto-Montage software (version 5.0), or a Leica DFC 425 camera in combination with the Leica Application Suite software (version 3.8). In verbatim descriptions of the Malagasy Ponera species, we follow terminology and character states established by Bolton and Fisher (2011).

Morphometric character recording

All measurements were taken by the first author using a Leica M165C stereomicroscope equipped with an ocular micrometer at a magnification of × 120. Body size dimensions are expressed in µm. Due to the abundance of worker specimens relative to queen and male specimens, the present revision is based on the worker caste only, which can further be justified by the fact that the name-bearing type specimens in this study belong to the worker caste. For the definition of morphometric characters, earlier protocols (Csősz & Seifert, 2003) were considered. Explanations and abbreviations for measured characters are given in Table 1. Morphometric data for each measured specimen are given in Supplementary Table S2.

Table 1 Abbreviations (Abbr.) for morphometric characters, and the protocol used to measure traits
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Further indices that have consistently been applied by earlier researchers (Perrault, 1993; Taylor, 1967; Wilson, 1957) are also provided in this work in order to improve integration of the new findings to earlier species concepts:

CI:

Cephalic index (CWb/CL × 100)

SI:

Scape index (SL/CWb × 100)

PNI:

Petiolar node index (PEW/MW × 100)

Statistical framework—hypothesis formation and testing

Generating prior species hypotheses via the combined application of NC clustering and PART. This method searches for discontinuities in continuous morphometric data, sorts all similar cases into the same cluster (see Seifert et al., 2014), and determines the ideal number of clusters. The present statistical framework follows the procedure applied in Csősz and Fisher (2016a, b). Advantages and limitations of the present procedure are discussed there.

Arriving at final species hypothesis using confirmatory LDA and LDA ratio extractor. To provide increased reliability of species delimitation, hypotheses for clusters and classification of cases via exploratory processes were confirmed by LDA leave-one-out cross-validation (LOOCV). Analyses were done in R (R Core Team, 2020). 

DNA sampling

We sequenced 658 base pairs (bp) of the mitochondrial cytochrome oxidase I (COI) gene from 182 Malagasy Ponera specimens. DNA extraction and COI sequencing were performed at the University of Guelph (Ontario, Canada) following the protocol described in Fisher and Smith (2008). An additional 60 Ponera sequences from different biogeographic regions, including Australasia and Indomalaya, and 3 outgroup sequences (Diacamma, Parvoponera, and Pseudoponera) were obtained from GenBank. Outgroup selection was based on Ponera phylogeny from Branstetter and Longino (2019). GenBank accession code and additional information for all sequences are given in Supplementary Table S3.

Molecular phylogenetic inference

We used molecular phylogenetic inference to confirm species taxonomic identification. Sequences were aligned using the Geneious Alignment algorithm implemented in Geneious 6.1.8 (Biomatters Ltd.). We included only unique haplotypes from each locality, resulting in a final alignment with 86 sequences. Phylogenetic analyses were performed using Bayesian inference in Mr. Bayes 3.2.7a and Maximum Likelihood using RAxML-NG online platform (https://raxml-ng.vital-it.ch/). The best-fit model of molecular substitution was estimated using PartitionFinder2 (Lanfear et al., 2016) under the Bayesian Information Criteria and linked branch lengths. The best partitioning scheme selected has 3 subsets, partitioning by codon position, as follows: GTR + G for first position, F81 for second position, and TRN + G for third position. Maximum likelihood bootstrap consensus tree was estimated using SumTrees 4.0.0 (Sukumaran & Holder, 2010, 2015). For Bayesian inference, two independent analyses of Metropolis coupling MCMC algorithm (MC3) ran for 106 generations, sampling every 500 generations, resulting in 1500 trees after a burn-in of 25%. Each analysis ran with 4 chains, 1 cold and 3 heated at a temperature of 0.1 and chain swap frequency of 1 each generation. Convergence of independent runs was assumed when the standard deviation of split frequencies reached values below 0.01.

Species concept

Integration of the evidence provided by different lines of evidence into an integrative species hypothesis is performed based on the principles advocated by Schlick-Steiner et al. (2010) and “integration by congruence” protocol introduced by Padial et al. (2010). In addition, we employ the universal GAGE species concept formulated by Seifert (2020), which represents the most widely used and accepted theoretical and practical indications in ant taxonomy.

Results

The exploratory NC-clustering, in combination with two hypothesis-free partitioning methods “hclust” and “kmeans,” concordantly returned three completely separated clusters (Fig. 1) in Malagasy Ponera samples based on 10 morphometric characters. The confirmatory LDA including the pessimistic LOOCV confirmed this pattern showing complete classification success. The type specimens (four syntype specimens of P. swezeyi are nested in one of the clusters, while the holotype of P. petila and the type series of P. bableti are nested together in another). These types have also been classified along with the relevant cluster with posterior p = 1, when type specimens were set to wildcard in LDA, i.e., no grouping label was added for type specimens. The third cluster endemic to Seychelles is considered a new species. Though this species clearly belongs to the P. clavicornis group, no similar available species could be identified using the literature (Leong et al., 2019; Perrault, 1993; Taylor, 1967; Wilson, 1957). This species is named Ponera adumbrans sp. n. reflecting its restriction to Seychelles islands.

Fig. 1
figure 1

Dendrogram solution for Malagasy Ponera species. Sample information in the dendrogram follows this format: final species hypothesis and CASENT number as a unique sample identifier followed by the capitalized geographic region separated by a hyphen. Two out of three columns of color bars represent prior species hypothesis resulted by method PART using two cluster methods “part.hclust” and “part.kmeans” (for additional information see text). Final species hypothesis bar shows classification of samples after confirmation by cross-validated LDA. Different colors distinguish species. Ponera petila: dark blue, P. adumbrans sp. n.: green, P. swezeyi: light blue. Types are marked by asterisks

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Phylogenetic analyses corroborate this finding, showing three independent and monophyletic clusters from the Malagasy region (Fig. 2). We found complete agreement between monophyly of clusters in the molecular phylogeny and the quantitative morphology-based cluster delimitation protocols. Taking all of these lines of evidence into account, we consider the three clusters to be three species.

Fig. 2
figure 2

Phylogeny of the Malagasy Ponera fauna. Bayesian inference phylogeny of Ponera COI sequences. Numbers associated to branches indicate Bayesian posterior probabilities and maximum likelihood bootstrap values. Only values greater than 50% are shown. Scale bar represents the number of substitutions per site. Different colors distinguish species. Ponera petila: dark blue, P. adumbrans sp. n.: green, P. swezeyi: light blue

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The three Ponera species distributed in the Malagasy region also differ in qualitative diagnostic features and body ratios (for body ratios, see Table 2).

Table 2 Mean of morphometric ratios calculated for each species on individual level. Morphometric trait ratios and ± SD are provided in the upper row, and minimum and maximum values are given in parentheses in the lower row
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Synopsis of Malagasy Ponera species


adumbrans Csősz & Fisher sp. n. (Fig. 3A–C)


petila Wilson, 1957 (Fig. 4A–C)


swezeyi (Wheeler, 1933) (Fig. 5A–C)

Fig. 3
figure 3

A–C Ponera adumbrans sp. n. paratype worker (CASENT0159966). Head in full-face view (A), dorsal view of the body (B), lateral view of the body (C)

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Fig. 4
figure 4

A–C Ponera petila non-type worker (CASENT0059796). Head in full-face view (A), dorsal view of the body (B), lateral view of the body (C)

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Fig. 5
figure 5

A–C Ponera swezeyi non-type worker (CASENT0135035). Head in full-face view (A), dorsal view of the body (B), lateral view of the body (C)

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Key to workers of the Malagasy Ponera species

  1. 1.

    Dark brown species (Fig. 3A–C). The largest species in the region, head width (CWb): > 400 µm [447, 478].


    …adumbrans sp. n.

    • Workers yellow to light brown (Figs. 4A–C and 5A–C). Small species (CWb): < 400 µm [291, 339]…2

  2. 2.

    Anterolateral and posterior surface of petiolar node meet in rounded transition (Fig. 4C). Larger species (CWb): 333 µm [323, 339]. Scape longer (SL/PEL): 1.99 [1.86, 2.09], [5–95% percentiles: 1.92, 2.08] …petila Wilson (1957).

Posterior surface of petiolar node bearing a ridge or fine vertical carina demarcating the posterior and lateral surfaces (Fig. 5C). Smaller species (CWb): 306 µm [291, 323]. Scape shorter (SL/PEL): 1.79 [1.68, 1.91], [5–95% percentiles: 1.71, 1.89]…swezeyi (Wheeler, 1933).


Ponera adumbrans Csősz & Fisher sp. n.


(Fig. 3A–C, Table 2)

Type material investigated

Holotype

Seychelles: CASENT0160838, collection code: BLF23554, Silhouette Island, on ridge toward Mont Corgat, [forest, sifted litter, leaf mold, rotten wood], -4.49537, 55.23946, alt. 445 m, B.L. Fisher et al., 2010.01.28, (3w, CASC);

Paratypes

Six workers with the same label data as the holotype under CASENT codes: Seychelles: CASENT0160837, collection code: BLF23554, (1w, CASC); CASENT0160840, collection code: BLF23554, (1w, CASC); CASENT0159923, collection code: BLF23458, (1w, CASC); CASENT0159088, collection code: BLF23558, (1w, CASC); CASENT0159966, collection code: BLF23434, (1w, CASC); CASENT0158808, collection code: BLF23254, (1w, CASC); CASENT0159375, collection code: BLF24028 (1w, CASC).

Etymology

The specific name "adumbrans" is a Latin singular present active participle in the nominative case that means “obscuring or silhouetting.” It refers to the obscure origin of this species in the Malagasy region and the type locality, Silhouette Island.

Description of workers

General appearance

Small species, absolute cephalic size (CS): 533 µm [518, 550]. Body color brown to black. Body concolorous, with antennae, funiculus, and legs lighter.

Head

Small, Head width (CWb): 462 µm [447, 478]; and conspicuously longer than broad, Cephalic index (CI): 77 [75, 78]. Frontal lobe distance vs. absolute cephalic size (FRS/CS): 0.25 [0.24, 0.26]. Head dorsum coarsely punctate. Anterior clypeal margin with an inconspicuous median indentation or notch. Eyes absent, occasionally 1 to 3 facets are visible. Scape longer, Scape index (SI): 93 [90, 96]; when laid straight back from its insertion the apex falls near, but does not reach, the midpoint of the posterior margin in full-face view. Mandibles with 3 distinct apical teeth occupying half of the masticatory border.

Mesosoma

Pronotal-mesonotal articulation present and developed across dorsum of mesosoma; always a strongly defined groove that conspicuously interrupts the surface. Metanotal groove absent. Dorsal surface of mesosoma coarsely punctate, dull. Lateral surface of pronotum finely punctate or areolate, dull. Mesopleural sculpture punctate to areolate, dull; metapleural sculpture longitudinally rugulose, partly shiny.

Petiole

Petiolar node squamiform, large; petiole width vs. absolute cephalic size (PEW/CS): 0.55 [0.52, 0.58]; broader than long, (PEW/PEL): 1.34 [1.31, 1.41]; anterior face of node widely rounded, the sides usually very divergent posteriorly. Petiolar node in profile relatively high and moderately long, with a rather short and weakly convex dorsum. Dorsal region of petiole smooth to finely punctate, shiny. Anterior and posterior faces of node usually clearly convergent dorsally. Lateral surface of node meets the posterior surface in a rounded transition without a cuticular ridge or transverse carina. Subpetiolar process absent to moderately developed, if present, its apex forms a right angle.

Differential diagnosis

This species cannot be confused with other Malagasy Ponera species due to its dark brown color in contrast to the yellowish brown color of P. petila and P. swezeyi and its larger body size relative to the latter two species. Worldwide, this species most resembles the Indo-Australian P. clavicornis Emery (1900), but P. adumbrans sp. n. clearly differs from its congener in shape, color, and size characteristics. The two species exhibit non-overlapping ranges of morphometric ratios: P. adumbrans has a shorter head (cephalic index, CI: 77 [75, 78]) than P. clavicornis (CI: 81–85, see Taylor, 1967), and the scape of P. adumbrans is longer (SI: 93 [90, 96]) than that of P. clavicornis (SI: 80–89, see Taylor, 1967).

Distribution

Known only from the Seychelles islands Silhouette and Mahé. 


Ponera petila Wilson (1957)


Ponera petila Wilson (1957: 368)


Ponera bableti Perrault (1993: 334 syn. nov)


(Fig. 4A–C, Table 2)

Type material investigated

Holotype of Ponera petila

Papua New Guinea: MCZ-ENT00030124, lower Busu River, Huon Pen. N.G., [lower rainforest,], V-/0-55 #999, E.O. Wilson, (1w, MCZ, MCZ-ENT00030124) [examined].

Holotype and paratypes of Ponera bableti

Fangataufa, “mers” 1987 “unintelligible text”, Ponera bableti Perrault (1993) det T. Ramage, (6w, MNHN, holotype: EY25377, paratypes EY25378, EY25379, EY25327, EY25328, EY25329) [Examined, measured by Quentin Rome based on the same character recording protocol defined in this paper, MNHN].

Other material morphometrically examined

Mauritius (8w), Seychelles (17w), Society Islands, French Polynesia (1w). For the full list of material, see Supplementary Table S1.

Description of workers

General appearance

Small species, absolute cephalic size (CS): 386 µm [372, 393]. Body color yellow to light brown. Body concolorous.

Head

Small, Head width (CWb): 333 µm [323, 339]; and conspicuously longer than broad, Cephalic index (CI): 76 [74, 77]. Frontal lobe distance vs. absolute cephalic size (FRS/CS): 0.22 [0.20, 0.24]. Head dorsum coarsely punctate. Anterior clypeal margin lacks a median indentation or notch. Eyes absent, occasionally 1 to 3 facets are visible. Scape short, Scape index (SI): 85 [82, 88]; when laid straight back from its insertion the apex falls far short of the midpoint of the posterior margin in full-face view. Mandibles with 3 distinct apical teeth occupying half of the masticatory border.

Mesosoma

Pronotal-mesonotal articulation present and moderately developed across dorsum of mesosoma; sometimes a weakly defined shallow groove visibly interrupts the surface. Metanotal groove inconspicuous, rarely absent. Dorsal surface of mesosoma punctate, slightly shiny. Lateral surface of pronotum finely punctate, ventral area smooth and shiny. Mesopleural sculpture inconspicuous, medial and ventral part smooth and shiny; metapleural sculpture inconspicuously punctate, centrally smooth and shiny.

Petiole

Petiolar node not squamiform, moderately large; petiole width vs. absolute cephalic size (PEW/CS): 0.50 [0.48, 0.53]; broader than long, (PEW/PEL): 1.35 [1.28, 1.45]; anterior face of node bluntly rounded, the sides usually slightly divergent posteriorly. Petiole node in profile moderately low and long, with a relatively short and weakly convex dorsum. Dorsal region of petiole smooth to finely punctate, shiny. Anterior and posterior faces of node usually weakly convergent dorsally, sometimes nearly parallel. Lateral surface of node meets the posterior surface in rounded transition without cuticular ridge or transverse carina. Subpetiolar process developed, its apex forms a right angle (rarely acute angle).

Differential diagnosis

In the Malagasy region, P. petila can only be confused with P. swezeyi; relevant diagnostic characters are discussed under diagnosis of the latter species. Worldwide, P. petila workers differ in size from all other species but P. szentivanyi Wilson, (1957). The latter species is reported to have a wider head (CWb: 340 µm, see Wilson, 1957) than P. petila (CWb: 333 µm [323, 339]), but the scape index (SI) of the P. szentivanyi is considerably larger (SI: 94) than that of P. petila (SI: 85 [82, 88]).

Distribution

In the Malagasy region, this species is distributed in Mauritius and Seychelles. Outside the region, it is known from Papua New Guinea and the Society Islands (French Polynesia).


Ponera swezeyi (Wheeler, 1933)


Pseudocryptopone swezeyi Wheeler (1933: 16)


Ponera swezeyi: Wilson (1957)


(Fig. 5 A–C, Table 2)

Type material investigated

Syntypes

Hawaii, USA: CASENT0249111, Is. Oahu, R. H. Van Zwaluwenburg, (1w, BPBM, CASENT0249111) [examined]; MCZ-ENT00593416, Is. Oahu, R. H. Van Zwaluwenburg, (3w, MCZC, MCZ-ENT00593416) [examined];

Other material morphometrically examined

Comores (16w), Madagascar (47w), Mauritius (5w), Mayotte (8w), Queensland, Australia (5w), Réunion (7w) Seychelles (11w). For the full list of material, see Supplementary Table S1.

Description of workers

General appearance

Small species, absolute cephalic size (CS): 358 µm [343, 376]. Body color yellow to light brown. Body concolorous.

Head

Small, Head width (CWb): 306 µm [291, 323]; and conspicuously longer than broad, Cephalic index (CI): 74 [70, 79]. Frontal lobe distance vs. absolute cephalic size (FRS/CS): 0.21 [0.19, 0.23]. Head dorsum coarsely punctate. Anterior clypeal margin lacks a median indentation or notch. Eyes absent, occasionally 1 to 3 facets are visible. Scape short, Scape index (SI): 83 [79, 87]; when laid straight back from its insertion the apex falls far short of the midpoint of the posterior margin in full-face view. Mandibles with 3 distinct apical teeth occupying half of the masticatory border.

Mesosoma

Pronotal-mesonotal articulation present and moderately developed across dorsum of mesosoma; sometimes a weakly defined shallow groove visibly interrupts the surface. Metanotal groove inconspicuous, rarely absent. Dorsal surface of mesosoma punctate, slightly shiny. Lateral surface of pronotum finely punctate, ventral area smooth and shiny. Mesopleural sculpture inconspicuous, medial and ventral part smooth and shiny; metapleural sculpture inconspicuously punctate, centrally smooth and shiny.

Petiole

Petiolar node not squamiform, moderately large; petiole width vs. absolute cephalic size (PEW/CS): 0.47 [0.43, 0.51]; slightly broader than long, (PEW/PEL): 1.20 [1.08, 1.35]; anterior face of node bluntly rounded, the sides usually slightly divergent posteriorly. Petiole node in profile relatively low and long, with a moderately long and weakly convex dorsum. Dorsal region of petiole smooth to finely punctate, shiny. Anterior and posterior faces of node usually weakly convergent dorsally, sometimes nearly parallel. Posterior surface of node bearing cuticular ridge or a fine vertical carina demarcating the posterior and lateral surfaces. Subpetiolar process well developed, its apex forms an acute angle.

Differential diagnosis

In the Malagasy region, this species can only be confused with P. petila, but petiole characters help distinguish these two species: in P. swezeyi, the anterolateral and posterior surfaces of petiolar node meet in sharp vertical ridges, while the lateral and posterior petiolar surfaces of P. petila meet in a rounded transition. Size of workers may also provide clues for identification: head width (CWb) of P. swezeyi is smaller 306 µm [291, 323]) than that of P. petila (333 µm [323, 339]). Worldwide, P. swezeyi is the smallest species within the tenuis group. Size variance detected in a relatively large pool (n = 105) of P. swezeyi workers was found negligible (CWb: 291 µm to 323 µm) allowing for separation of P. swezeyi workers from that of other species. Only one species, P. szaboi Wilson, 1957) overlapping with P. swezeyi (CWb: 306 µm [291, 323]), but the petiole of P. swezeyi species is considerably wider (PNI: 77–83) than that of P. szaboi (PNI: 61–65, see Taylor, 1967).

Distribution

Ponera swezeyi is known to occur in the eastern coast of Madagascar, Comoros, Mauritius, Mayotte, Reunion, and Seychelles in the Malagasy region. Moreover, populations are known from Queensland (northeastern Australia), Hawaii, Christmas Island, Japan (Fiji Island), Hawaii, Japan (Ogasawara Islands), Samoa, Solomon Islands, and Tanzania (Fisher & Bolton, 2016; Leong et al., 2019).

Discussion

Altogether, three Ponera species were recognized in the Malagasy region via an integrative taxonomic protocol, P. petila Wilson, 1957, P. adumbrans sp. n., and P. swezeyi (Wheeler, 1933). Two of them (P. petila and P. swezeyi) belong to the predominantly Indo-Australian Ponera tenuis group. The third species, P. adumbrans sp. n., is morphologically close to the Indo-Malayan P. clavicornis. The two tenuis group species occupy both natural and semi-natural environments from low to high altitudes. The two tenuis group species occupy both natural and semi-natural environments from low to high altitudes. Ponera swezeyi is found widely in Madagascar and adjacent islands, while P. petila is known only from Mauritius and Seychelles. The P. adumbrans is endemic to Seychelles and typically occurs in higher altitudes.

The Indo-Australian origin of each Malagasy Ponera species has been supported by two lines of evidence: (a) Africa does not harbor native Ponera fauna (Fisher & Bolton, 2016), and no fossil records are known from the continent; (b) two out of the known three Malagasy Ponera species belong to the Indo-Australian Ponera tenuis group and are identical with two recent species, P. petila and P. swezeyi, while the third species, P. adumbrans, is morphologically closely related to the Papua New Guinean P. clavicornis Emery (1900), which further strengthens the Indo-Australian connection.