Shaped by the Sun: the effect of exposure to sunlight on the evolution of spider bodies.

Body temperature can strongly influence fitness. Some Sun-exposed ectotherms thermoregulate by adjusting body posture according to the Sun's position. In these species, body elongation should reduce the risk of heat stress by allowing the exposure of a smaller body area to sunlight. Therefore, selection should favour more elongated bodies in Sun-exposed than in Sun-protected species. Diurnal orb-web spider species that sit on their webs are more likely to be Sun-exposed, on average, than nocturnal or diurnal shelter-building species. We measured the body elongation of orb-web spiders (Araneae, Araneidae) across 1024 species and classified them as Sun-protected or exposed based on the literature. We found that Sun-exposed species evolved more elongate bodies than Sun-protected ones. Further, we built a model combining traditional heat transfer models with models of thermoregulatory postures in orb-web spiders and meteorological data. The model indicates that body elongation in large orb-web spiders decreases the risk of high body temperatures. Overall, our results suggest that Sun exposure influenced the evolution of body shapes of orb-web spiders.

Slit sense organ distribution on the legs of two species of orb-weaving spider (Araneae: Araneidae).

Biotic and abiotic mechanical stimuli are ubiquitous in the environment, and are a widely used source of sensory information in arthropods. Spiders sense mechanical stimuli using hundreds of slit sense organs (small isolated slits, large isolated slits, groups of slits and lyriform organs) distributed across their bodies and appendages. These slit sense organs are embedded in the exoskeleton and detect cuticular strain. Therefore, the spatial pattern of these sensors can give clues into how mechanical stimuli from different sources might be processed and filtered as they are transmitted through the body. Here, we map the distribution of slit sense organs on the legs in two species of orb-weaving spider, A. diadematus and T. edulis, in which slit sense organ distribution has not previously been investigated. We image the spiders' legs using scanning electron microscopy, and trace the position and orientation of slits on these images to describe the distribution and external morphology of the slit sense organs. We show that both species have a similar distribution of slit sense organs, with small isolated slits occurring in consistent lines parallel to the long axis of the legs, whilst large isolated slits, groups of slits and lyriform organs appear in fixed positions near the leg joints. Our findings support what has been described in the literature for several other species of spider, which indicates that slit organ arrangement is conserved across spiders in different evolutionary lineages and with disparate hunting strategies. The dispersed distribution of small isolated slits along the whole length of the leg may be used to detect large-scale strain of the leg segment as a result of muscle activity or internal changes in haemolymph pressure.

Nine new species of the spider family Araneidae (Arachnida, Araneae) from Xishuangbanna, Yunnan, China.

Nine new species of the orb-weaver spider family Araneidae Clerck, 1757 from Menglun Town, Xishuangbanna, Yunnan, China are described: Acusilastongi sp. nov. (♂♀), Chorizopesyui sp. nov. (♂♀), Chorizopesoidesguoi sp. nov. (♂♀), Deionecheni sp. nov. (♀), D.yangi sp. nov. (♂♀), Hypsosingapulla sp. nov. (♂♀), Mangorabaii sp. nov. (♂♀), M.cephala sp. nov. (♂♀) and Miloniagemella sp. nov. (♂♀). The genus Milonia Thorell, 1890 is recorded from China for the first time. The previous description of Chorizopesoideswulingensis (Yin, Wang & Xie, 1994) from Libo County, Guizhou by Mi and Wang (2018) refers to Chorizopesoidesannasestakovae sp. nov. (♂♀). Diagnostic photos of the habitus and copulatory organs of the new species are provided.

On nine species of the spider genus Eriovixia (Araneae, Araneidae) from Xishuangbanna, China.

Species of the genus Eriovixia Archer, 1951 from Menglun Town, Xishuangbanna, Yunnan, China are reviewed, including seven new species: E. ganae sp. nov. (♂♀), E. liuhongi sp. nov. (♂♀), E. tangi sp. nov. (♂♀), E. wangchengi sp. nov. (♂♀), E. yaoi sp. nov. (♂♀), E. yinae sp. nov. (♂♀) and E. zhengi sp. nov. (♂♀). The male of E. yunnanensis (Yin, Wang, Xie & Peng, 1990) is described for the first time. The previous description of E. yunnanensis from Tengchong, Yunnan by Mi et al. (2010) refers to E. pengi sp. nov. (♂♀). Diagnostic photos of the habitus and copulatory organs of the new species and E. yunnanensis from Xishuangbanna are provided.

The complete mitochondrial genome of Trichonephila clavipes (Araneae: Araneidae).

Trichonephila clavipes (Linnaeus, 1767) is known as a golden silk orb-weaver and belongs to the family Araneidae. T. clavipes is one of the few spider species whose genome has been reported and model organism for a molecular biology. Here, we present the complete mitochondrial genome sequence (mtDNA) of T. clavipes. The sequence was obtained using a long-read Nanopore technology and corrected with an Illumina technology. The circular genome is 14,902 bp in length, and the AT content was 77.21%. The T. clavipes mitochondrial genome contains 13 protein-coding genes (PCGs), 22 tRNA genes, and 2 rRNA genes. The majority of PCGs were found on the heavy strain.

Two hymenopteran egg sac associates of the tent-web orbweaving spider, Cyrtophora citricola (Forskål, 1775) (Araneae, Araneidae).

We report the discovery of two wasp species emerging from egg sacs of the spider Cyrtophora citricola (Forskål 1775) collected from mainland Spain and the Canary Islands. We identify one as Philolema palanichamyi (Narendran 1984) (Hymenoptera, Eurytomidae) and the other as a member of the Pediobius pyrgo (Walker 1839) species group (Hymenoptera, Eulophidae). This is the first report of Philolema in Europe, and the first documentation of hymenopteran egg predators of C. citricola. The latter finding is particularly relevant, given the multiple invasive populations of C. citricola in the Americas and the Caribbean, where neither egg sac predation nor parasitism is known to occur. We describe rates of emergence by Ph. palanichamyi from spider egg sacs collected from the southern coast of Spain and estimate sex ratios and body size variation among males and females. We also re-describe Ph. palanichamyi based on the female holotype and male paratype specimens.

Two new species of Araneus Clerck, 1757 (Araneae, Araneidae) and first description of A. wulongensis male from China.

Two new species of Araneus Clerck, 1757 are described: A. conexus sp. nov. (♂♀) and A. digitatus sp. nov. (♂♀) from Yunnan and Hubei provinces. The male of A. wulongensis Song & Zhu, 1992 is described here for the first time. All species treated in this study belong to A. strurmi species group. Detailed description and illustrations of somatic features, and copulatory organs as well as distribution maps are provided.

Argiope hoiseni, a new species of the spider genus Argiope (Araneae, Araneidae) from Peninsular Malaysia based on morphology and molecular analyses.

A new species of Argiope Audouin 1826, A. hoiseni new species is described from Perak and Selangor, Peninsular Malaysia based on morphology and DNA information of the mitochondrial (16S rRNA, COI and COII) and nuclear-encoded (H3A, 18S rRNA) molecular markers. Epigynal structure suggested Argiope hoiseni to be similar to A. jinghongensis Yin, Peng Wang 1994, A. luzona (Walckenaer 1841), A. pulchella Thorell 1881 and A. taprobanica Thorell 1887. Molecular sequence data including the new species inferred that it is monophyletic with an intraspecific variation of 0.87-3.59 % based on the 16S+COI+COII+H3A dataset. Phylogenetic analyses also revealed insights into the evolutionary lineages of Argiope species in Southeast Asia as well as corroborated recent taxonomic changes and species synonymies associated with Argiope. Two new distribution records were also reported for A. chloreis Thorell,1877 and A. doleschalli Thorell, 1873 in Peninsular Malaysia.

Mysmenidae, a spider family newly recorded from Tibet (Arachnida, Araneae).

The spider family Mysmenidae is reported from Tibet for the first time. Two new species, Chanea voluta sp. n. (male and female) and Mysmena lulanga sp. n. (male and female) are found in eastern Tibet in high altitude. Morphological descriptions, diagnoses and comparative photos are provided for the two new species.

An orb-weaver spider exploits an ant-acacia mutualism for enemy-free space.

Exploiters of protection mutualisms are assumed to represent an important threat for the stability of those mutualisms, but empirical evidence for the commonness or relevance of exploiters is limited. Here, I describe results from a manipulative study showing that an orb-weaver spider, Eustala oblonga, inhabits an ant-acacia for protection from predators. This spider is unique in the orb-weaver family in that it associates closely with both a specific host plant and ants. I tested the protective effect of acacia ants on E. oblonga by comparing spider abundance over time on acacias with ants and on acacias from which entire ant colonies were experimentally removed. Both juvenile and adult spider abundance significantly decreased over time on acacias without ants. Concomitantly, the combined abundance of potential spider predators increased over time on acacias without ants. These results suggest that ant protection of the ant-acacia Acacia melanocerus also protects the spiders, thus supporting the hypothesis that E. oblonga exploits the ant-acacia mutualism for enemy-free space. Although E. oblonga takes advantage of the protection services of ants, it likely exacts little to no cost and should not threaten the stability of the ant-acacia mutualism. Indeed, the potential threat of exploiter species to protection mutualisms in general may be limited to species that exploit the material rewards traded in such mutualisms rather than the protection services.

First description of the male with redescription of the female of Araneus strandiellus Charitonov, 1951 (Araneae, Araneidae).

Redescription of Central Asian orb-weaver Araneus strandiellus Charitonov, 1951, only known from the original description of female. The male of this species, previously unknown, is described here for the first time.

Evidência de aprendizagem na construção de teia na aranha Argiope Argentata (Araneae: Araneidae) / Evidence of learning in the web construction of the spider Argiope Argentata (Araneae: Araneidae)

We investigated the effects of past experience on the web construction by the spider Argiope argentata. The spiders were submitted to periods in horizontal position alternated with periods in vertical position (control phase). The observations revealed an improvement in the quality of the second vertical web when compared to the first; disordered web-building behavior when first in a horizontal phase, with resultant web deformities; improvements in web quality after successive web constructions in a horizontal phase; finally, we observed improvements in spiders' performance and a shorter time needed to build their webs when the spiders were submitted to the horizontal phase for the second time. The results suggest that improvements during the horizontal periods were due to changes in the building patterns in the early stages of spider web construction (mesh, frame and radius constructions). Our results favor the hypothesis that this improvement is due to past experience or learning.

Investigamos os efeitos de experiência passada na construção da teia da aranha Argiope argentata. As aranhas foram submetidas a períodos em suportes horizontais alternados por períodos de suportes verticais (condição controle). Os resultados revelaram melhora da primeira para a segunda teia vertical; desorganização do desempenho no primeiro contato com a condição horizontal; melhora do desempenho após sucessivas construções horizontais e finalmente melhor desempenho e menor latência de construção no segundo contato com a horizontal. Os resultados sugerem que a melhora, na condição de horizontalidade, decorre de uma mudança nos padrões iniciais da construção (feitura de amarras/quadro/raios) e apoiam a hipótese de que esta melhora seja um produto de experiência passada ou aprendizagem.