Research Article |
Andrés A. Ojanguren-Affilastro‡, Fermín M. Alfaro§|, Hernán A. Iuri‡, Bernardino Camousseigt-Montolivo¶, Jaime Pizarro-Araya#¤|§
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Corresponding author: Jaime Pizarro-Araya ( japizarro@userena.cl ) Academic editor: Danilo Harms
© 2025 Andrés A. Ojanguren-Affilastro, Fermín M. Alfaro, Hernán A. Iuri, Bernardino Camousseigt-Montolivo, Jaime Pizarro-Araya.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ojanguren-Affilastro AA, Alfaro FM, Iuri HA, Camousseigt-Montolivo B, Pizarro-Araya J (2025) Description of Brachistosternus pehuenche sp. nov. (Scorpiones, Bothriuridae), a new scorpion species from the upper Maule Valley, in the southern Chilean Andes. Zoosystematics and Evolution 101(3): 969-981. https://doi.org/10.3897/zse.101.146451
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Abstract
Brachistosternus pehuenche sp. nov. (Scorpiones, Bothriuridae) is described from the Mauline Andean forests of the northern Chilean Patagonia, located within the upper basin of the Maule Valley. Its unique geography and the discovery of this partial isolation, as a result of the surrounding higher altitudes, support the role of this valley as a biodiversity hotspot, fostering a variety of endemic epigean arthropods. The discovery of this third endemic scorpion species highlights the area’s ecological uniqueness. The species is most similar to Brachistosternus negrei, a species found in the southern Chilean forests, but distinct morphological traits, such as pigmentation patterns and metasomal structures, clearly separate the two. This study underscores the ecological value of the Maule Valley, which, despite its high endemism, remains unprotected and is subject to significant anthropogenic pressures, including agriculture, hydropower projects, and international transit routes. The need for conservation initiatives in this region is critical to preserve its exceptional biodiversity. This work not only adds to the taxonomy of Brachistosternus but also raises fundamental questions about the processes driving endemism in the Andes and the broader implications for the conservation of montane ecosystems.
Key Words
Area of endemism, Bothriuridae, Chile, Mauline woods, new species, Scorpiones
Introduction
Chile harbors a remarkably high diversity of epigean arthropods. Due to its particular geography, characterized by an extreme latitudinal gradient crossed by numerous transversal rivers and mountain chains, this country has several areas of endemism, each with their own arthropod communities (
The Andean Mauline forests of the upper basin of the Maule Valley (Fig.
The genus Brachistosternus is highly diversified in arid and semiarid areas of southern South America and is the dominant scorpion group in these extremely harsh environments (
Despite the remarkable biological diversity of the study area and its immense potential as a hotspot for endemic species, no formal actions have been taken to establish protected areas to safeguard this unique environment. The upper Maule Valley, with its distinctive geography and ecology, harbors a rich array of species that appear to be restricted to this region, underscoring its importance as a critical area for conservation. However, the lack of protection leaves this ecosystem vulnerable to escalating anthropogenic threats, including land-use changes, infrastructure development, and resource exploitation.
In this contribution, we present the formal description of Brachistosternus pehuenche sp. nov., a scorpion species likely endemic to the upper Maule Valley. This finding reinforces the hypothesis that the region constitutes an area of endemism for epigean arthropods, driven by its partial isolation and unique environmental conditions. Furthermore, we emphasize the urgent need for conservation actions, including the establishment of protected areas, to ensure the preservation of this exceptional ecosystem and its endemic biota, which are at an increased risk from human activities.
Methods
The specimens examined are deposited in the following collections:
Museo Argentino de Ciencias Naturales “Bernardino Rivadavia,” Buenos Aires, Argentina (
All the new material reported here was collected by the authors; most specimens were collected at night using UV detection. Some specimens were also collected in the daytime under logs or stones. All measurements, taken using an ocular micrometer, are presented in millimeters (mm). The descriptive terminology follows
Results
Systematics
Brachistosternus pehuenche sp. nov.
Type material.
Chile, Maule Region (VII), Maule Valley, Fundo La Escuadra: Holotype ♂ (
Etymology.
The specific epithet “pehuenche” is a noun in apposition referring to the Pehuenche International Pass between Argentina and Chile, in the northern Patagonia, where this and other endemic scorpion species have been collected. Pehuenche is also the name of the indigenous people of this area, belonging to the Mapuche cultural group.
Diagnosis.
Brachistosternus pehuenche sp. nov. is most similar to B. negrei, which is the only Brachistosternus species occurring in nearby areas of the south-central Chilean woods. Both species can be easily distinguished by several morphological characters. Brachistosternus pehuenche, on one hand, has tergites that bear two lateral spots, with pigment occupying most of the posterior lateral margins and leaving a median unpigmented stripe (Figs
A‒D. Brachistosternus pehuenche sp. nov. A. Tergites IV and V, pigment pattern; B. Metasomal segments I–IV, pigment pattern; C. Metasomal segment V, male, dorsal aspect, and Androvestigia; D. Metasomal segment V, male, ventral aspect; E‒H. Brachistosternus negrei; E. Tergites IV and V, pigment pattern; F. Metasomal segments I–IV, pigment pattern; G. Metasomal segment V, male, dorsal aspect and Androvestigia; H. Metasomal segment V, male, ventral aspect. Scale bars: 1 mm.
Description.
Based on the male holotype (
Measurements (mm) for Brachistosternus pehuenche sp. nov. male and female paratypes (MACN).
| Brachistosternus pehuenche sp. nov. | ||
|---|---|---|
| Paratype ♂ | Paratype ♂ | |
| Total length | 45.18 | 46.89 |
| Carapace, length | 5.25 | 5.74 |
| Carapace, anterior width | 4.04 | 4.61 |
| Carapace, posterior width | 5.66 | 6.46 |
| Mesosoma, total length | 12.23 | 16.63 |
| Metasoma, total length | 27.70 | 26.32 |
| Metasomal segment I, length | 3.39 | 2.91 |
| Metasomal segment I, width | 3.64 | 3.88 |
| Metasomal segment I, height | 2.83 | 2.91 |
| Metasomal segment II, length | 4.04 | 3.64 |
| Metasomal segment II, width | 3.47 | 3.39 |
| Metasomal segment II, height | 2.75 | 2.91 |
| Metasomal segment III, length | 4.12 | 3.88 |
| Metasomal segment III, width | 3.39 | 3.31 |
| Metasomal segment III, height | 2.67 | 2.75 |
| Metasomal segment IV, length | 4.44 | 4.44 |
| Metasomal segment IV, width | 3.23 | 3.23 |
| Metasomal segment IV, height | 2.66 | 2.59 |
| Metasomal segment V, length | 5.25 | 4.85 |
| Metasomal segment V, width | 3.31 | 3.23 |
| Metasomal segment V, height | 2.59 | 2.42 |
| Telson, length | 6.38 | 6.30 |
| Vesicle, width | 2.51 | 2.51 |
| Vesicle, height | 2.02 | 2.18 |
| Femur, length | 4.20 | 3.72 |
| Femur, width | 1.13 | 1.37 |
| Tibia, length | 4.04 | 3.64 |
| Tibia, width | 1.54 | 1.70 |
| Chela, length | 7.67 | 7.11 |
| Chela, width | 2.26 | 1.94 |
| Chela, height | 3.67 | 2.34 |
Color
: Base color yellowish, with dark brown pigmentation pattern in pedipalps, carapace, tergites, metasoma, and legs; the remaining, yellowish without dark spots (Fig.
Chelicerae : Anterior margin of movable finger curved, with two small subdistal teeth.
Pedipalps
: Femur (Fig.
Carapace : Anterior margin convex, with six setae and a well-developed median bulge. Surface slightly granular in the median area, almost smooth in females; lateral and posterior surfaces more densely granular. Anterior longitudinal sulcus, posterior longitudinal sulcus, and lateral sulci very well developed. Median ocular tubercle well developed, placed slightly in front of the middle of the carapace, smooth surface except for its posterior margin, which is slightly granular and bears two setae, one behind each eye; inter-ocular sulcus only barely visible in the posterior margin, median ocelli medium large, ca. two diameters apart, and aiming laterally. Lateral ocelli pattern type 3A, with three small, similarly sized, lateral ocelli on each side of carapace; anterior and posterior situated in the same horizontal axis, median ocellus situated slightly below them; posterior ocellus situated one diameter apart from anterior and median ocelli.
Legs : Surfaces smooth. Basitarsi, each with two well-developed pedal spurs, being the internal one about 30 percent smaller compared to the external one in legs I and II, and slightly smaller in legs III and IV. Telotarsi ventrolaterally compressed, dorsally with a row of setae, ventrally each with an incomplete ventro-median row of poorly developed hyaline setae, and paired rows of ventro-submedian setae; telotarsus III with the following counts of setae: dorsal setae: 7–9 (N = 15; median = 19); ventrointernal setae: 4–6 (N = 15; median = 6); ventroexternal setae: 2–5 (N = 15; median = 3). Ungues slightly curved, external ungues being about 30 percent smaller compared to the internal in legs I and II, and being equal in size in legs III and IV. Pseudoniquium and distal projection well developed.
Pectines : Well developed. Tooth count, males: 29–33 (N = 10; median = 33); females: 28–32 (N = 10; median = 31).
Sternum
: With two small subtriangular lateral lobes, each with a macroseta clearly thicker and blunter than the remaining ventral macrosetae (
Genital opercula : Sclerites subtriangular, with a posterior lobe.
Tergites : I–VI, with two anterior dorso-submedian setae; surfaces, smooth in females, barely granular in the postero-lateral margins in males; VII granular in the posterior half, with paired lateral carinae in posterior half of segment, and paired submedian carinae restricted to the posterior margin, with two barely visible sub-median bulges in the posterior median third of the segment.
Sternites : III–VI surface densely granular in posterior half in males, smooth in females, with medium-sized elliptical spiracles and small and shallow ventro-submedian pits; VII granular in males, smooth in females.
Metasoma
: Metasomal segment I, dorsal surface barely granular, median sulcus well developed and smooth; DL carinae well developed, granular, extending only on the posterior half of the segment, with a DL macrosetae; lateral surface granular between LM and DL carinae, the rest smooth; LM carinae granular, restricted to the posterior half of the segment, with a medial seta; granular LIM carinae present in the posterior half of the segment, with a seta near the posterior margin; ventral surface smooth in females, densely granular in males, without VL carinae, with two VL macrosetae on each side (in smooth pits in males), and with two VL and two VSM macrosetae in the posterior margin. Metasomal segments II and III similar to segment I, but less granular and with less developed carinae, ventrally with one or two pairs of VSM setae. Metasomal segment IV, dorsal surface smooth, DL carinae granular, occupying almost the entire length of the segment, with a DL median macroseta and a posterior accessory dorsal carina; lateral margins granular, more so in males, with three LSM setae, ventrally smooth, with abundant scattered macrosetae. Metasomal segment V, elongated (Fig.
Telson
: Vesicle globose, slightly more so in males, surface slightly granular in antero-ventral margin, the rest smooth; ventrally with two VSM shallow furrows, laterally with a longitudinal wide smooth furrow; males with two barely visible dorsal glandular areas which occupy most of the dorsal margin. Aculeus longer than the vesicle, shallowly curved, more so in females (Fig.
A‒G. Brachistosternus pehuenche sp. nov. A. Right pedipalp chela, female, internal aspect; B. Right pedipalp chela, male, internal aspect; C. Right pedipalp chela, male, ventral aspect; D. Right pedipalp chela, male, external aspect; E. Right pedipalp chela, male, dorsal aspect; F. Right pedipalp patella, male, external aspect; G. Right pedipalp femur, male, external aspect. Scale bars: 1 mm.
Hemispermatophore
: Basal portion (stem) well developed. Distal lamina (stalk) well developed, slightly curved medially (Fig.
Distribution.
Brachistosternus pehuenche is currently known only from the upper basin of the Maule Valley, located in the Maule Region of central Chile. This region lies within the Andean Mauline forests, characterized by a complex landscape of valleys and mountain ranges ranging from approximately 1000 to 1800 m a.s.l. The scorpion has been collected in a variety of microhabitats within this elevation range, including shrub steppes, gramineous steppes, and dry woodlands, but it appears to be more abundant in open environments like shrub and gramineous steppes.
The distribution of B. pehuenche appears to be tightly restricted to the upper Maule Valley, as no specimens have been found in adjacent areas despite extensive fieldwork performed by our group in the different seasons of the year (see below). For example, surveys conducted in the Altos del Lircay Reserve to the north and the Pejerrey area to the south failed to detect the species, further supporting the hypothesis of its endemism to the Maule Valley. Instead, B. negrei, a closely related species, dominates in these neighboring regions, underscoring the geographic and ecological isolation of B. pehuenche.
Ecology.
Brachistosternus pehuenche inhabits the distinctive landscape of the Andes Maulinos Botanical Formation, which represents the southernmost boundary of high Andean steppes. This region is characterized by a unique combination of dry woods, shrub steppes, and gramineous steppes, with plant species such as Chuquiraga oppositifolia, Gochnatia foliosa, Proustia cuneifolia (Asteraceae), Discaria articulata (Rhamnaceae), and Festuca acanthophylla (Poaceae). These diverse habitats not only host the scorpion but also shape a mosaic critical to its survival.
Interestingly, B. pehuenche has demonstrated ecological flexibility by thriving across these environments, with a marked preference for shrub and gramineous steppes over wooded areas. Its seasonal activity pattern occurs in spring and summer, a period shared with U. trewanke but not U. pehuenche, which remains active during winter. This temporal niche differentiation may reduce direct competition among sympatric scorpion species in the region.
Field studies also suggest that B. pehuenche contributes significantly to the local arthropod trophic web during its active months due to its abundance, being one of the most common predators among epigean arthropods. However, winter surveys have consistently failed to locate active specimens, indicating a strict period of dormancy. This activity pattern aligns with ecological pressures such as temperature extremes and resource availability, common in high-altitude Andean ecosystems.
Discussion
The restricted distribution of B. pehuenche emphasizes the ecological importance of the upper Maule Valley as a critical center for biodiversity and endemism in the southern Andes. This region harbors a unique combination of habitats that sustain a wealth of endemic species yet faces escalating anthropogenic pressures. Key threats include agricultural expansion, hydropower development, and the construction of international transit routes, all of which contribute to the fragmentation and degradation of its fragile ecosystems.
The discovery of B. pehuenche not only enhances our understanding of the biodiversity within this Andean hotspot but also underscores the pressing need for comprehensive ecological studies. Mapping the precise geographic range and identifying key microhabitats of the species are essential for understanding its ecological requirements and resilience to environmental changes. Moreover, population assessments are imperative to determine its conservation status under the IUCN criteria.
This scenario highlights the urgent necessity for implementing conservation measures aimed at preserving the upper Maule Valley. These efforts should include the designation of protected areas, the promotion of sustainable land-use practices, and the integration of biodiversity considerations into regional development policies. Without such actions, the long-term survival of B. pehuenche and other endemic taxa in this ecologically significant area remains uncertain.
The upper Maule Valley has emerged as a hotspot of endemism, with B. pehuenche as the latest addition to its growing list of exclusive taxa. This area’s partial geographic isolation, framed by transverse mountain chains, has facilitated the evolution of unique biota. Previous discoveries of Alsodes pehuenche (Cei 1976) (a frog) (
Targeted collection campaigns have further validated this view. While neighboring regions like Altos del Lircay and Pejerrey host other Brachistosternus species (e.g., B. negrei), B. pehuenche appears confined to the upper Maule Valley, reinforcing its endemic status. This restricted distribution, coupled with its habitat specificity, underscores the ecological and evolutionary importance of the region.
Despite its biological significance, the upper Maule Valley faces mounting environmental threats. Intensive agricultural practices and hydropower development along the Maule River contribute to habitat degradation. Furthermore, the heavy vehicular traffic along the Pehuenche International Pass introduces additional ecological disturbances. The absence of formal protection exacerbates these risks, leaving endemic species like B. pehuenche vulnerable to habitat loss and population declines.
In conclusion, B. pehuenche exemplifies the biodiversity and endemism that make the upper Maule Valley a critical area for conservation. Its discovery not only enriches our understanding of Bothriuridae diversity but also highlights the urgent need to establish protected areas. Safeguarding this unique ecosystem would ensure the survival of its endemic species and preserve an irreplaceable component of Chile’s natural heritage.
Acknowledgements
Our special thanks to the staff of the Los Cipreses hydroelectric power plant, especially to Christian Cartes for his help with logistics (La Escuadra, ENEL). We also thank Víctor Bravo-Naranjo for his photographic assistance and Juan Calderon for his help during the field work. Project funded by Environment & Permitting - HSEQ, Enel Green Power & Thermal Generation (ENEL). J.P-A would like to thank the Academic Excellence Scholarship (B134) from the Academic Vice-Rector’s Office, Research and Postgraduate Studies of the Universidad Santo Tomás, Santiago, Chile, and the ANID doctoral fellowship 2024-21241400. F.M.A. also thanks the ANID doctoral fellowship 2023-21230592. We are also indebted to three reviewers: Carlos Santibáñez-López, Edmundo González-Santillán, and Lorenzo Prendini for their helpful comments on the early draft of the manuscript.
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