Wildlife value of tropical forest restoration
Selective logging at the Stability of Altered Forest Ecosystems project site, Sabah, Malaysian Borneo.
Habitat degradation in tropical forests continues to harm vital ecosystems. Because such degradation affects approximately 4 billion ha of tropical forest, global efforts to increase conservation and restoration are underway. Nicolas Deere et al. (pp. 26254–26262) identified areas of degraded tropical forests in Borneo that, if conserved or restored, would particularly benefit wildlife. The authors combined camera trap data collected between 2015 and 2017 with 3D landscape mapping to examine species’ responses to changes in forest structure due to logging. Many of the 28 tropical mammals species examined were high conservation value species. Mammals tended to disproportionately occupy structurally complex, multidimensional environments with tall canopies, diverse niches, and increased plant area, all of which are indicators of healthy forest habitat. However, mammals avoided forested areas undergoing structural simplification. Forests in such areas were characterized by open canopies and reduced vegetation density, both of which are byproducts of excessive logging. The findings highlight the importance of maintaining forests, given that mammals’ active avoidance of heavily degraded areas may lead to failing ecosystems and defaunation, according to the authors. — M.S.
Cocaine-seeking during sustained abstinence
Overcoming cocaine use disorder requires achieving and sustaining abstinence, the latter of which typically presents the greater challenge. Although studies have established that drug-associated cues induce craving that strengthens during sustained abstinence, the neurobiological basis of intensified drug seeking remains unclear. Craig Werner, Swarup Mitra, et al. (pp. 26460–26469) examined the role of the dorsal hippocampus (DH)—a brain region tied to context-dependent cocaine seeking—in relapse vulnerability. Using a rat model, the authors found that a member of the transforming growth factor-β superfamily, activin A, is both elevated in the DH and regulates drug seeking on day 30 but not day 1 of abstinence. Furthermore, the authors report how activin A regulates cocaine seeking on day 30 via NMDA receptors, which mediate a reward-and-motivation signaling pathway that is remodeled by cocaine use. Synaptic strength increases through time in the DH during abstinence, and, by day 30, the DH connections to the lateral septum, a brain region implicated in vulnerability to cocaine relapse, are also strengthened. The findings illuminate the role of the DH in cocaine seeking during abstinence, according to the authors. — T.J.
Dietary isotopic signatures in Amazonian and African rainforests
Inuya River, Peruvian Amazonia.
Closed canopy rainforests influence Earth’s climate and biodiversity. However, researchers lack comprehensive data about how these important ecosystems function, hampering attempts to identify closed canopy rainforests in the fossil record and chart their evolution. Julia Tejada et al. (pp. 26263–26272) used isotopic analysis to construct a model of feeding ecology in modern mammals from western Amazonia. The authors compared the results with similar analyses of extant mammals in equatorial Africa, a proxy used to identify past closed canopy rainforests on all continents. The comparison revealed the median value of dietary δ13C—a carbon isotope that tracks plant consumption—does not differ significantly between Amazonian and African closed canopy rainforests and may be representative of mammalian herbivores in any closed canopy rainforest. However, the Amazonian mammals in the study lacked the highly negative dietary δ13C values found in their African counterparts, a hallmark feature often used to infer closed canopy rainforests in fossil records. According to the authors, the study suggests that current assumptions about ecological niches, feeding habits, and isotopic signatures may need to be reassessed. — T.J.
Dynamic evolution of Y chromosome in great apes
Although the human Y chromosome is critical for fertility and a useful tracer for population genetic studies, its evolutionary history in great apes remains unclear. DNA sequence data of the Y chromosome—available for humans, chimpanzees, and gorillas—has further confounded researchers, revealing that the human Y chromosome shares more gene content with gorillas than with chimpanzees, even though humans share a more recent ancestor with chimpanzees. Monika Cechova, Rahulsimham Vegesna, et al. (pp. 26273–26280) decoded the Y chromosomes from bonobos and orangutans and added the data to published human, chimpanzee, and gorilla Y assemblies to produce a Y chromosome data set that includes all genera of extant great apes. Analyzing the data, the authors report that the Y chromosome in chimpanzees and bonobos, members of the genus Pan, experienced rapid DNA changes and high gene death rates, consistent with mating practices in which sperm from different males compete to fertilize the same egg. Furthermore, the characteristic Y chromosome structure, containing DNA repeats and duplicate genes, was likely present in the common ancestor of great apes. The findings demonstrate the dynamic nature of Y chromosome evolution and suggest new areas of study of nonhuman great ape reproduction, according to the authors. — T.J.
Magnitude and impact of Maya volcanic eruption
Ilopango volcano, the source of the 431 CE Tierra Blanca Joven (TBJ) eruption.
Large areas of El Salvador and its Maya sites show a layer of ash from the Tierra Blanca Joven eruption of the Ilopango volcano, which would have rendered areas within 80 km of the vent uninhabitable for decades during the Early Classic Period, around 300–600 CE. Pinpointing the date of the eruption can help clarify its impacts on climate and society. Victoria Smith et al. (pp. 26061–26068) combined archaeological evidence with analysis of ice cores in Greenland to date the eruption to within 2 years of 431 CE. Based on modeling of tephra deposition, the authors report that the eruption would have sent a 45 km plume into the atmosphere. The authors identified volcanic glass shards matching those from the eruption in a dated ice core from Greenland at 431 CE. Radiocarbon data from trees in the area of the eruption and sulfur spikes in Antarctic ice cores corresponded to the same time period. The authors note that the date also corresponds to archaeological records that suggest cessation of Maya pottery production in El Salvador. According to the authors, the magnitude of the eruption would have cooled the atmosphere by 0.5 °C for a few years, and the major effects were largely limited to the local region. — T.H.D.