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Comment on Seri Masran and Ab Majid 2017

Tseng SP, Yang CS

J Med Entomol, 2017 09 01;54(5):1107-1108.
PMID: 28874021 DOI: 10.1093/jme/tjx136
Fulltext Fitness advantages of the biased use of paired laterally symmetrical penises in an insect

Kamimura Y, Yang CS, Lee CY

J Evol Biol, 2019 08;32(8):844-855.
PMID: 31081978 DOI: 10.1111/jeb.13486

The evolution of laterality, that is the biased use of laterally paired, morphologically symmetrical organs, has attracted the interest of researchers from a variety of disciplines. It is, however, difficult to quantify the fitness benefits of laterality because many organs, such as human hands, possess multimodal functions. Males of the earwig Labidura riparia (Insecta: Dermaptera: Labiduridae) have morphologically similar laterally paired penises, only one of which is used for inseminating the female during a single copulation bout, and thus provide a rare opportunity to address how selection pressure may shape the evolution of population-level laterality. Our population studies revealed that in 10 populations, located at 2.23-43.3° north, the right penis is predominantly used for copulating (88.6%). A damaged penis was found in 23% of rare left-handers, suggesting that the left penis can function as a spare when the right one is damaged. By pairing L. riparia females with surgically manipulated males, we found that males forced to use the right penis outperformed left-handed males in copulation (the probability of establishing genital coupling during the 1-hr observation period: odds ratio [OR] of 3.50) and insemination (probability of transferring a detectable amount of sperm: OR of 2.94). This right-handed advantage may be due to the coiled morphology of the sperm storage organ with a right-facing opening. Thus, female genital morphology may play a significant role in the evolution of handedness and may have acted as a driving force to reduce penis number in related taxa.
Complete genome sequences of two novel dicistroviruses detected in yellow crazy ants (Anoplolepis gracilipes)

Lee CC, Lin CY, Hsu HW, Yang CS

Arch Virol, 2020 Nov;165(11):2715-2719.
PMID: 32776255 DOI: 10.1007/s00705-020-04769-2

We report two novel RNA viruses from yellow crazy ants, (Anoplolepis gracilipes) detected using next-generation sequencing. The complete genome sequences of the two viruses were 10,662 and 8,238 nucleotides in length, respectively, with both possessing two open reading frames with three conserved protein domains. The genome organization is characteristic of members of the genus Triatovirus in the family Dicistroviridae. The two novel viruses were tentatively named "Anoplolepis gracilipes virus 1" and "Anoplolepis gracilipes virus 2" (AgrV-1 and AgrV-2). Phylogenetic analyses based on amino acid sequences of the non-structural polyprotein (ORF1) suggest that the two viruses are triatovirus-like viruses. This is the first report on the discovery of novel triatovirus-like viruses in yellow crazy ants with a description of their genome structure (two ORFs and conserved domains of RNA helicase, RNA-dependent RNA polymerase, and capsid protein), complete sequences, and viral prevalence across the Asia-Pacific region.
Fulltext Population genetic structure of the globally introduced big-headed ant in Taiwan

Liu KL, Tseng SP, Tatsuta H, Tsuji K, Tay JW, Singham GV, et al.

Ecol Evol, 2022 Dec;12(12):e9660.
PMID: 36582779 DOI: 10.1002/ece3.9660

Global commerce and transportation facilitate the spread of invasive species. The African big-headed ant, Pheidole megacephala (Fabricius), has achieved worldwide distribution through globalization. Since the late 19th century, Taiwan has served as a major seaport because of its strategic location. The population genetic structure of P. megacephala in Taiwan is likely to be shaped by international trade and migration between neighboring islands. In this study, we investigated the population genetics of P. megacephala colonies sampled from four geographical regions in Taiwan and elucidated the population genetic structures of P. megacephala sampled from Taiwan, Okinawa, and Hawaii. We observed a low genetic diversity of P. megacephala across regions in Taiwan. Moreover, we noted low regional genetic differentiation and did not observe isolation by distance, implying that long-distance jump dispersal might have played a crucial role in the spread of P. megacephala. We sequenced the partial cytochrome oxidase I gene and observed three mitochondrial haplotypes (TW1-TW3). TW1 and TW3 most likely originated from populations within the species' known invasive range, suggesting that secondary introduction is the predominant mode of introduction for this invasive ant. TW2 represents a novel haplotype that was previously unreported in other regions. P. megacephala populations from Taiwan, Okinawa, and Hawaii exhibited remarkable genetic similarity, which may reflect their relative geographic proximity and the historical connectedness of the Asia-Pacific region.
Fulltext Worker reproduction of the invasive yellow crazy ant Anoplolepis gracilipes

Lee CC, Nakao H, Tseng SP, Hsu HW, Lin GL, Tay JW, et al.

Front. Zool., 2017;14:24.
PMID: 28503187 DOI: 10.1186/s12983-017-0210-4

BACKGROUND: Reproductive division of labor is one of the key features of social insects. Queens are adapted for reproduction while workers are adapted for foraging and colony maintenance. In many species, however, workers retain functional ovaries and can lay unfertilized male eggs or trophic eggs. Here we report for the first time on the occurrence of physogastric workers and apparent worker reproduction in the invasive yellow crazy ant Anoplolepis gracilipes (Fr. Smith). We further examined the reproductive potential and nutritional role of physogastric workers through multidisciplinary approaches including morphological characterization, laboratory manipulation, genetic analysis and behavioral observation.
RESULTS: Egg production with two types of eggs, namely reproductive and trophic eggs, by physogastric workers was found. The reproductive egg was confirmed to be haploid and male-destined, suggesting that the workers produced males via arrhenotokous parthenogenesis as no spermatheca was discovered. Detailed observations suggested that larvae were mainly fed with trophic eggs. Along with consumption of trophic eggs by queens and other castes as part of their diet, the vital role of physogastric workers as "trophic specialist" is confirmed.
CONCLUSION: We propose that adaptive advantages derived from worker reproduction for A. gracilipes may include 1) trophic eggs provisioned by physogastric workers likely assist colonies of A. gracilipes in overcoming unfavorable conditions such as paucity of food during critical founding stage; 2) worker-produced males are fertile and thus might offer an inclusive fitness advantage for the doomed orphaned colony.