Testing the Role of Male-Male Competition in the Evolution of Sexual Dimorphism: A Comparison Between Two Species of Porcelain Crabs

Theory predicts marked sexual dimorphism in terms of body size and body structures used as weapons (e.g. chelipeds) in gonochoric species with intense male sexual competition for receptive females and reduced or no sexual dimorphism in species where competition among males is trivial. We tested this hypothesis using a pair of closely-related species of symbiotic porcelain crabs as a model. In one species that inhabits sea anemones solitarily, competition among males for receptive females is unimportant. In a second species that dwells as dense aggregations on sea urchins, malemale competition for sexual partners is recurrent. We expected considerable sexual dimorphism in body size and weaponry in the urchin-dwelling crab and reduced sexual dimorphism in the anemone-dwelling crab. In agreement with expectations, in the urchin-dwelling crab, male body size was, on average, larger than that of females and males invested considerably more to cheliped length than females. Also supporting theoretical considerations, in the anemone-dwelling crab, sexual dimorphism in terms of body size was not detected and differences between the sexes in investment to cheliped length were minor. Interestingly, chelipeds were more developed both in males and females of the anemone-dwelling crab than in the urchin-dwelling crab as a result of the importance of these structures for monopolization of their naturally scarce anemone hosts. Another difference between the studied species was the existence of two clearly distinguishable ontogenetic phases in males of the urchin-dwelling crab but not in males of the anemone-dwelling crab. Whether the two different male morphs display different male reproductive strategies in the urchin-dwelling crab remains to be addressed. Other conditions that might additionally explain the observed differences in sexual dimorphism (e.g. female mate choice) between the studied species remain to be explored. © 2011 The Linnean Society of London

Complete mitochondrial genomes of two species of Stichopathes Brook, 1889 (Hexacorallia: Antipatharia: Antipathidae) from Rapa Nui (Easter Island)

We report the complete mitochondrial genomes of two antipatharian species, Stichopathes sp. SCBUCN-8849 and Stichopathes sp. SCBUCN-8850, collected between 120 and 180 m depth off Rapa Nui (∼ −27.1°, −109.4°). The size of the two mitogenomes are 20,389 bp (29.0% A, 15.2% C, 19.9% G, and 35.9% T) and 20,463 bp (29.0% A, 15.3% C, 19.9% G, and 35.8% T), respectively. Both mitogenomes have the classic Hexacorallia gene content of 13 protein-coding, two rRNA, and two tRNA genes plus a COX1 intron with embedded HEG as found in the Antipathidae and other antipatharian families

First Ecological Characterization of Whip Black Coral Assemblages (Hexacorallia: Antipatharia) in the Easter Island Ecoregion, Southeastern Pacific

One of the main priorities of marine scientific research is to provide practical information and guidance for biodiversity conservation and management. In this context, the identification of key and fragile habitat-forming species is particularly important. Despite their ecological importance, whip corals in the order Antipatharia remain poorly studied around the world, and especially in the South Pacific. During recent expeditions to explore mesophotic and deep benthic habitats around Rapa Nui (Easter Island), dense assemblages of whip black corals were observed in situ. We here report the first detailed description of the distribution and abundance of these black coral assemblages and their associated fauna and habitat. These descriptions were based on analysis of video surveys collected on 67 remotely operated vehicle dives conducted in 2014 through 2019 at three sites (Pukao seamount, Apolo peak, and Rapa Nui Island shelf and slope) within the Easter Island Ecoregion at depths between 50 and 330 m. At least four morphotypes (yellow, red, white/orange, and Pukao) of unbranched black corals were detected. Each morphotype had polyps arranged in a single row on only one side of the corallum, a diagnostic morphological character currently assigned to the antipatharian genus Stichopathes. Samples of the yellow and red morphotypes were collected and studied using morphological and molecular techniques. These analyses indicate that the genus Stichopathes is not monophyletic and requires further revisions, a conclusion that is consistent with previous studies. Extensive fields of whip black corals, primarily of the yellow and red morphotype, were present at 28 sites from 60 to 245 m on rocky substrates, coarse sand, or rhodoliths. Densities of these assemblages per frame were up to 58.2 ± 5.2 colonies m–2 (average: 13.2 ± 0.8), which represent some of the highest reported densities for black corals to date. Numerous faunal groups, including ophiuroids, echinoids, and fishes, were associated with these whip black coral assemblages. Our observations should be considered in future management and conservation efforts around Rapa Nui, where a multi-use marine protected area was established in 2018, as well as in adjacent international waters that remain unprotected but likely harbor similar assemblages

A search for ultra-high-energy photons at the Pierre Auger Observatory exploiting air-shower universality

The Pierre Auger Observatory is the most sensitive detector to primary photons with energies above ∼0.2 EeV. It measures extensive air showers using a hybrid technique that combines a fluorescence detector (FD) with a ground array of particle detectors (SD). The signatures of a photon-induced air shower are a larger atmospheric depth at the shower maximum (X$_{max}$) and a steeper lateral distribution function, along with a lower number of muons with respect to the bulk of hadron-induced background. Using observables measured by the FD and SD, three photon searches in different energy bands are performed. In particular, between threshold energies of 1-10 EeV, a new analysis technique has been developed by combining the FD-based measurement of X$_{max}$ with the SD signal through a parameter related to its muon content, derived from the universality of the air showers. This technique has led to a better photon/hadron separation and, consequently, to a higher search sensitivity, resulting in a tighter upper limit than before. The outcome of this new analysis is presented here, along with previous results in the energy ranges below 1 EeV and above 10 EeV. From the data collected by the Pierre Auger Observatory in about 15 years of operation, the most stringent constraints on the fraction of photons in the cosmic flux are set over almost three decades in energy

Study on multi-ELVES in the Pierre Auger Observatory

Since 2013, the four sites of the Fluorescence Detector (FD) of the Pierre Auger Observatory record ELVES with a dedicated trigger. These UV light emissions are correlated to distant lightning strikes. The length of recorded traces has been increased from 100 μs (2013), to 300 μs (2014-16), to 900 μs (2017-present), to progressively extend the observation of the light emission towards the vertical of the causative lightning and beyond. A large fraction of the observed events shows double ELVES within the time window, and, in some cases, even more complex structures are observed. The nature of the multi-ELVES is not completely understood but may be related to the different types of lightning in which they are originated. For example, it is known that Narrow Bipolar Events can produce double ELVES, and Energetic In-cloud Pulses, occurring between the main negative and upper positive charge layer of clouds, can induce double and even quadruple ELVES in the ionosphere. This report shows the seasonal and daily dependence of the time gap, amplitude ratio, and correlation between the pulse widths of the peaks in a sample of 1000+ multi-ELVES events recorded during the period 2014-20. The events have been compared with data from other satellite and ground-based sensing devices to study the correlation of their properties with lightning observables such as altitude and polarity