A reassessment of Dioon merolae (Zamiaceae) leads to the description of Dioon salas-moralesae, a new cycad species from Southeastern Oaxaca, Mexico

The cycad genus Dioon comprises 17 species from Mexico and Honduras, all of them delimited based on their morphological variation and geographic distribution. A recent evaluation of the biological variation among Dioon populations from Oaxaca and Chiapas, Mexico, demonstrated that the concept of the species Dioon merolae actually consists of three lineages that should be recognized as different taxa. One lineage was already described as Dioon oaxacensis, leaving the concept of Dioon merolae comprising two lineages distributed on both sides of the Isthmus of Tehuantepec. However, there are conspicuous morphological differences between these two lineages. Here, we tested whether such a differentiation within the concept of Dioon merolae merits the differentiation of two different taxa. We evaluated the qualitative and morphometric variation among populations belonging to the Dioon merolae lineages, and compared it with the closely related species Dioon oaxacensis. Morphological observations and statistical tests demonstrated that the populations of southeastern Oaxaca, traditionally considered as part of Dioon merolae, represent a distinct species that we described as Dioon salas-moralesae. Identifying the diagnostic characters of this new species helps enable an understanding of the criteria that should be considered to delineate the boundaries between other cycad species.

Mitochondrial DNA indicate paraphyletic relationships and resolve disjunct distributions in the Neotoma mexicana species group

Woodrats (genus Neotoma) comprise 24 species found primarily in the US and Mexico. The Neotoma mexicana species group reaches its southernmost distribution in the highlands of southern Mexico and Central America. Previous research suggested that N. mexicana has a disjunct distribution, and it, N. ferruginea and N. picta have allopatric distributions and limit each other around the lowlands of the Isthmus of Tehuantepec. However, these hypotheses were suggested with incomplete subspecific sampling near the isthmus. We used new samples of N. m. parvidens from the Oaxacan Sierra Madre del Sur and N. m. tropicalis from the Sierra Norte de Oaxaca to assess their taxonomic affinity. With new sequences of the mitochondrial cytochrome-b gene, we found that both subspecies belong to N. ferruginea, not N. mexicana. We therefore suggest that N. mexicana is continuously distributed from the US to the Transmexican Volcanic Belt, N. picta inhabits the Guerreran Sierra Madre del Sur, and N. ferruginea ranges from the Oaxacan Sierra Madre del Sur to Central America. Our findings indicate that the Isthmus of Tehuantepec did not promote speciation in these woodrats, but we did detect intraspecific genetic differentiation between samples of N. ferruginea from east and west of the isthmus.

A re-examination of the molecular systematics and phylogeography of taxa of the Peromyscus aztecus species group, with comments on the distribution of P. winkelmanni

The objectives of this study are to examine the available molecular data from the mitochondrial cytochrome-b gene (Cytb) and a concatenated dataset with this gene and two nuclear introns (Adh-1-I2 and Fgb-I7) to reexamine the systematic and phylogeographic conclusions reached by Sullivan et al. (1997) concerning the Peromyscus aztecus species group. The divergence of samples of P. aztecus oaxacensis across the Isthmus of Tehuantepec are further examined and taxonomic revisions are suggested. In addition, this study reviews the sources of data that lead to the conclusion that P. winkelmanni occurred in the Sierra Madre del Sur in Guerrero including a morphometric examination of a reported voucher. Bayesian and maximum likelihood analyses were conducted on a dataset of 31 Cytb sequences of all taxa in the P. aztecus group except for P. a. cordillerae and a concatenated dataset including five individuals of this group. Representative taxa of the P. boylii, P. mexicanus, and P. truei groups were included in both analyses. Body and cranial measurements of the voucher of the P. winkelmanni from Guerrero from which a Cytb sequence is reported to have been obtained was compared with measurements from specimens taken from the vicinity of Dos Aguas, Michoacán, including the type locality. We identified seven instances involving problematic identifications in GenBank. Once these issues were addressed, well-supported monophyletic sister clades of the P. aztecus and P. boylii species groups were recovered from phylogenetic analyses of Cytb sequences (Fig 1). Phylogenetic analyses of the Cytb and the concatenated datasets recover similar topologies that support the relationships of taxa of the aztecus group proposed by an earlier molecular study. Populations of P. a. oaxacensis southeast of the Isthmus of Tehuantepec represent a distinct species. Measurements of the voucher from Guerrero identified as the source of a P. winkelmanni Cytb sequence are smaller than P. winkelmanni for several characters. The divergent populations of P. a. oaxacensis from southeast of the Isthmus of Tehuantepec are recognized as two subspecies of P. cordillerae, P. c. cordillerae and P. c. hondurensis, whereas those northwest of the Isthmus are retained as P. a. oaxacensis. The lack of genetic divergence observed between P. a. evides and P. a. oaxacensis questions whether these two taxa should continue to be recognized as separate subspecies. Northern and southern populations of P. spicilegus demonstrate moderate divergence and additional examination of morphological and molecular differentiation within this taxon is warranted. The distribution of P. winkelmanni should be restricted to the vicinity of Dos Aguas, Michoacán, due to the lack of a voucher specimen that would confirm its reported occurrence in Guerrero.

Land grabbing or value grabbing? Land rent and wind energy in the Isthmus of Tehuantepec, Oaxaca

The Isthmus of Tehuantepec in Oaxaca is the first region in Mexico with a large-scale wind energy development. The region holds 60% of the country’s installed capacity, but the new infrastructure has faced opposition from sectors of the local population concerned about wind farms’ social and environmental impacts. The opposition and ensuing conflicts have been widely studied; some of these studies have framed wind energy as part of the recent cycle of land grabbing. Nevertheless, this literature has overlooked landholders’ acceptance of wind energy. This paper aims to address this gap and argues that the main driver of the land grabbing process is land rent. The paper draws on recent insights from political ecology that highlight that the commodification of nature is predicated on rent. The paper uses the notion of value grabbing to look at the social struggles over property rights in the Isthmus and the conflicts for the increase and distribution of rents from wind energy.

Reconsidering the Age and Typological Character of “Pox Pottery” from Guerrero, Mexico

We revisit the age and typological character of “Pox Pottery” that was reported in the 1960s by Charles Brush who considered it to be uniquely early (~2440 BC). Investigating the same two sites in coastal Guerrero where Brush excavated, we recovered Early Formative ceramics, some with the “pox” attribute. Here, we report potsherd frequencies for these deposits at both sites according to regional ceramic typologies, as well as AMS 14C dates used to establish a Bayesian stratigraphic chronology for each site to better constrain the age of these Early Formative period deposits. We argue that “Pox Pottery” is not a ceramic type per se and that the “pox” attribute occurs in multiple Early Formative period ceramic types. The earliest pottery is similar to other Red-on-Buff ceramic traditions from the Central Mexican Highlands and west of the Isthmus of Tehuantepec. Our chronological work demonstrates that these ceramics date between 1820 and 1400 cal BC, consistent with other recent studies indicating an early age of Red-on-Buff ceramics and suggesting shared cultural traditions distinct from the contemporary Locona interaction sphere that emerged in parallel.