RESUMEN
Mutual reinforcement between abiotic and biotic factors can drive small populations into a catastrophic downward spiral to extinction-a process known as the "extinction vortex." However, empirical studies investigating extinction dynamics in relation to species' traits have been lacking.We assembled a database of 35 vertebrate populations monitored to extirpation over a period of at least ten years, represented by 32 different species, including 25 birds, five mammals, and two reptiles. We supplemented these population time series with species-specific mean adult body size to investigate whether this key intrinsic trait affects the dynamics of populations declining toward extinction.We performed three analyses to quantify the effects of adult body size on three characteristics of population dynamics: time to extinction, population growth rate, and residual variability in population growth rate.Our results provide support for the existence of extinction vortex dynamics in extirpated populations. We show that populations typically decline nonlinearly to extinction, while both the rate of population decline and variability in population growth rate increase as extinction is approached. Our results also suggest that smaller-bodied species are particularly prone to the extinction vortex, with larger increases in rates of population decline and population growth rate variability when compared to larger-bodied species.Our results reaffirm and extend our understanding of extinction dynamics in real-life extirpated populations. In particular, we suggest that smaller-bodied species may be at greater risk of rapid collapse to extinction than larger-bodied species, and thus, management of smaller-bodied species should focus on maintaining higher population abundances as a priority.
RESUMEN
PURPOSE: Thymomas are epithelial neoplasms that represent the most common thymic tumors in adults. These tumors have been shown to harbor a relatively low mutational burden. As a result, there is a lack of genetic alterations that may be used prognostically or targeted therapeutically for this disease. Here, we describe a recurrent gene rearrangement in type B2 + B3 thymomas. PATIENTS AND METHODS: A single index case of thymoma was evaluated by an RNA-based solid fusion assay. Separately, tissues from 255,008 unique advanced cancers, including 242 thymomas, were sequenced by hybrid capture-based next-generation DNA sequencing/comprehensive genomic profiling of 186 to 406 genes, including lysine methyltransferase 2A (KMT2A) rearrangements, and a portion were evaluated for RNA of 265 genes. We characterized molecular and clinicopathologic features of the pertinent fusion-positive patient cases. RESULTS: We identified 11 patients with thymomas harboring a gene fusion of KMT2A and mastermind-like transcriptional coactivator 2 (MAML2). Fusion breakpoints were identified between exon 8, 9, 10, or 11 of KMT2A and exon 2 of MAML2. Fifty-five percent were men, with a median age of 48 years at surgery (range, 29-69 years). Concurrent genomic alterations were infrequent. The 11 thymomas were of B2 or B3 type histology, with 1 case showing foci of thymic carcinoma. The frequency of KMT2A-MAML2 fusion was 4% of all thymomas (10 of 242) and 6% of thymomas of B2 or B3 histology (10 of 169). CONCLUSION: KMT2A-MAML2 represents the first recurrent fusion described in type B thymoma. The fusion seems to be specific to type B2 and B3 thymomas, the most aggressive histologic subtypes. The identification of this fusion offers insights into the biology of thymoma and may have clinical relevance for patients with disease refractory to conventional therapeutic modalities.
