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CO1 barcode analysis and extensive SEM data revisit the old world Micropholcus spiders

CO1 barcode analysis and extensive SEM data revisit the old world Micropholcus spiders

NEWS - Micropholcus Deeleman-Reinhold & Prinsen, 1987, is one of only two genera of Pholcidae known in both the Old and New Worlds. However, there are large morphological and ecological differences among geographically separated species groups and molecular data to unite all these species into a single genus.

The researchers reviewed and redescribed the Old World Micropholcus from four previously known species and twelve new species from Saudi Arabia (M. dhahran, M. harajah, M. alfara, M. abha, M. tanomah, M. bashayer, M. maysaan), Oman (M. darbat, M. shaat), Morocco (M. ghar, M. khenifra), and the Philippines (M. bukidnon).

Bernhard Huber and Guanliang Meng from the Zoological Research Museum Alexander Koenig in Bonn, conducted analyses based on CO1 barcodes, extensive SEM data, and first records of Acroceridae (Diptera) larvae in Pholcidae, extracted from book lungs. The interspecific distance had an average value of 19.8% (3.4–25.7%). Only seven of the 371 distance values were at or below 10%. All of these referred to species in the Saudi Arabian group.

In the northern Saudi Arabian group, the distance between M. maysaan and the other two species (M. tanomah, M. bashayer) ranged from 8.0–10.0%. The distance between M. tanomah and M. bashayer was 10.2%. Despite these low values, the two best-scoring partitions in the ASAP analysis separated these three species.

In the southern Saudi Arabian group, M. alfara and M. dhahran were very close (3.4%); the distances of these two species to M. harajah were only 6.1–6.7%. Most partitions in the ASAP analysis separated M. alfara and M. dhahran as a single species and only the best (and worst) separated M. harajah as a distinct species.

From a morphological perspective, there were consistent differences among specimens for the different nominal species. These differences are at about the same level of uniqueness as among relatives in many genera of Pholcidae. Furthermore, the traits of each are remarkably homogeneous.

However, from a molecular perspective, they suggest distinct species boundaries, particularly among the southern Saudi Arabian group. The genetic distance of 3.4–6.7% is clearly below the problematic range of overlap between intra- and interspecific distances for Pholcidae.

The ASAP analysis suggests that this group contains only one or two species, not three. The researchers give more weight to the morphological evidence. Almost every location in the highlands with suitable habitat in Saudi Arabia has its own Micropholcus ‘species’ and it is expected that the extent to Yemen will dramatically increase the number of species.

Micropholcus in the Old World has a wide geographic range but appears to be largely restricted to semiarid regions, where the spiders lead a solitary life in caves, in cave-like chambers under rocks, and in rock depressions.

The Arabian Peninsula and Morocco are particularly species-rich, suggesting that this genus must also be present in suitable habitats across a large but under-sampled area, including M. bukidnon. The Philippines extends the distribution of the genus far eastward, but the species are morphologically exceptional and rely only on molecular evidence.

Micropholcus is highly diverse in southwestern Saudi Arabia as one of the richest biodiversity regions in the Arabian Peninsula and high species richness is also found in Yemen. The Saudi Arabian species appear to be restricted to the highlands (above 1200 m). The Yemeni species are often morphologically distinct but genetically very close.

Acroceridae flies primarily attack cursorial and fossorial spider species, probably due to the larval strategy for locating spider hosts. Researchers have documented the first case of Acroceridae larvae developing in the book lungs of web-building Pholcidae. Acroceridae larvae spend the day at the top of the dome-shaped web that is firmly attached to a rock surface.

Original research

Huber BA, Meng G (2024). Old World Micropholcus spiders, with first records of acrocerid parasitoids in Pholcidae (Araneae). ZooKeys 1213: 95-182, DOI:10.3897/zookeys.1213.133178

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