Sustained force production by the jaw-adductor muscles of a megalophagous frog, Ceratophrys cranwelli.

Most frogs have weak jaws that play a relatively minor role in tongue-mediated prey capture. Horned frogs (Ceratophrys spp.), however, follow the projection of a large tongue with a vice-like grip of their jaws to hold and immobilize prey. Prey include relatively large vertebrates, which they may restrain for minutes to possibly hours. High endurance behaviors, such as prolonged biting, require that muscles be capable of sustained force production. The feeding behavior of Ceratophrys suggests that their jaw-adductor muscles may be capable of powering sustained bites for long periods. We examined the capacity for sustained bite force by conducting an in situ experiment during which we measured bite force while bilaterally and supramaximally stimulating the jaw-adductor muscles of euthanized Cranwell's horned frogs (C. cranwelli). Muscles were stimulated for at least 60 min with a series of tetanic trains, with one experiment lasting over 6 h. We found that a significant sustained force develops during the first few minutes of the experiment, and this force is present between tetanic trains when the muscles are not being stimulated. The sustained force persists long after tetanic forces are barely detectable. The observed sustained force phenomenon parallels that observed for the jaw-adductor muscles of alligator lizards (Elgaria), another animal capable of sustained biting. The ability to bite with sustained and significant force by C. cranwelli may be facilitated by a configuration of different muscle fiber types, such as slow tonic fibers, as well as specializations in the muscle fibers that mitigate the effects of fatigue.

Female-female aggression in the Gila monster (Heloderma suspectum).

Historically, the role of aggression in the social lives of animals overwhelmingly focused on males. In recent years, however, female-female aggression in vertebrates, particularly lizards, has received increasing attention. This growing body of literature shows both similarities and differences to aggressive behaviours between males. Here, we document female-female aggression in captive Gila monsters (Heloderma suspectum). Based on four unique dyadic trials (eight adult female subjects), we developed a qualitative ethogram. Unexpected and most intriguing were the prevalence and intensity of aggressive acts that included brief and sustained biting, envenomation, and lateral rotation (i.e. rolling of body while holding onto opponent with closed jaws). Given specific behavioural acts (i.e. biting) and the results of bite-force experiments, we postulate that osteoderms (bony deposits in the skin) offer some degree of protection and reduce the likelihood of serious injury during female-female fights. Male-male contests in H. suspectum, in contrast, are more ritualized, and biting is rarely reported. Female-female aggression in other lizards has a role in territoriality, courtship tactics, and nest and offspring guarding. Future behavioural research on aggression in female Gila monsters is warranted to test these and other hypotheses in the laboratory and field.

Trisomy 10 and acute myeloid leukemia.

We report the second case of trisomy 10 as the sole abnormality in acute erythroblastic leukemia (AML M6). Trisomy 10 is a rare recurring numerical chromosomal abnormality is probably linked to a myeloblast subset with CD7+ and CD33+ immunophenotype. Most of the 15 cases reported to date in the literature have been M0, M1, or M2, with one showing AML M6 morphology.