Dra. Rodríguez-San Martin, Sara

Prey profitability is one of the most important factors influencing prey selection. This factor varies along with both prey size and handling time. Thus, large prey are generally highly profitable for consumers and boost competition. Kleptoparasitism is a form of competition in which an individual steals food previously obtained by another individual. Accordingly, handling large prey should increase the likelihood of kleptoparasitism occurrence, but these relationships remain poorly understood. Here, we studied kleptoparasitism occurrence by the Brown‐Hooded Gull (Chroicocephalus maculipennis – Laridae) on Whimbrels (Numenius phaeopus hudsonicus – Scolopacidae) preying on intertidal Mole Crabs (Emerita analoga) in a wave‐exposed sandy beach in southern Chile. Generalized linear models, fitted to data from focal‐individual video sequences, showed that kleptoparasitism probability had a positive sigmoidal response to handling time. Moreover, with an increase of 1 s in handling time, a Whimbrel doubled its probability of being kleptoparasitized. Additionally, the odds of being kleptoparasitized were 17% higher with an increase of 10 mm in prey length and 47% higher with an increase of one gull per host. However, the effect of handling on kleptoparasitism probability slightly decreased (2%) with an increase of 10 mm in prey size class. Our results suggest the existence of a threshold time in which consumers can handle their prey before kleptoparasitism probability is too high. Nevertheless, Whimbrel's mean intake rate reached 0.15 ± 0.13 kJ s−1, allowing Whimbrels to theoretically meet their energetic requirements despite losing some prey to kleptoparasites. This study provides new insight into a common form of competition among consumers, highlighting the importance of prey handling time for shorebirds with a restricted foraging time driven by tidal cycles.

Previous descriptions of Corynosoma bullosum (Linstow, 1892) show that specimens vary greatly in the proportions of different body structures, measurements of females and males, number of rows of hooks, and egg measurements, among other features. We redescribe this species from specimens found in southern elephant seal faeces from King George Island. We also provide a molecular characterization, in addition to 5.8S and internal transcribed spacer (ITS) existing sequences. We examined 41 elephant seals, and 30 adult acanthocephalans were found in 15 of them. The specimens were identified as belonging to the genus Corynosoma due to each having a tubular body with an inflated anterior part forming a thorny disk and the posterior part bearing somatic spines on the ventral surface, and genital spines surrounding the genital pore. Individual morphology corresponded to C. bullosum: large size, marked sexual dimorphism, and proboscis with 16–18 rows of spines with 11–15 spines per row. The molecular profile of three specimens of C. bullosum was analysed using 18S rDNA. We inferred phylogenetic relationships of the family Polymorphidae using maximum likelihood and Bayesian inference. We provide an updated morphological redescription for C. bullosum including electron microscopy photographs and molecular data. The 18S gene sequences showed low genetic variation and supported that C. bullosum is a sister to Corynosoma australe.