Hyobanche hanekomii (Orobanchaceae), a new species from the Western Cape of South Africa

Andrea D. Wolfe. 2018. Phytotaxa 340 (1): 093–097. DOI:10.11646/phytotaxa.340.1.8

Abstract

The new species Hyobanche hanekomii is described and illustrated. It is somewhat intermediate in appearance between H. sanguinea and H. atropurpurea, but can be distinguished from both in several morphological characters that are presented. The new species occurs in the Cape fold Belt Mountains of the northwest part of the Western Cape.

Jennifer K Hellmann, Ian M Hamilton. 2018. Behavioral Ecology, ary006, DOI:10.1093/beheco/ary006

Abstract

In several cooperatively breeding species, subordinates that do not help sufficiently are punished or evicted from the group by dominant individuals. The credibility of dominant eviction threats may vary with the social context beyond the group level: when subordinates can easily breed in a neighboring territory, dominants may be less able to demand help from subordinates. Further, dominant ability to enforce subordinate cooperation may be reduced when it is difficult to replace evicted subordinates or in small groups where each subordinate makes a large contribution to group productivity. Here, we develop a 2-player game theoretic model to examine how the social context influences subordinate help and the threshold of help at which dominants evict subordinates. In contrast to predictions, we found that dominants demand more help when dominants are less able to replace evicted subordinates, suggesting that dominants punish a dereliction of helping behavior more strongly when they are unable to compensate for the loss of an evicted subordinate. In single sealed-bid games, subordinates help less than the fitness costs they impose on dominants and help does not vary with subordinate breeding opportunities outside the group. However, when subordinates can plastically increase help in response to demanding dominants (akin to pay-to-stay dynamics), subordinates provide more help overall, but decrease their help as breeding opportunities outside of the group increase. Our results demonstrate the importance of incorporating negotiation into theoretical models of helping strategies and demonstrate that plasticity is a key mechanism underlying pay-to-stay mechanisms of cooperation.

Jonathan Z. Shik, Angelo Concilio, Thomas Kaae, Rachelle M. M. Adams. 2018. DOI:10.1111/een.12512

Abstract

When parasites exploit mutualisms involving food exchange, they can destabilise the partnership with costs to interacting partners. For instance, the ant Sericomyrmex amabilis farms fungal symbionts to produce food, but, in so doing, attracts parasitic Megalomyrmex symmetochus guest ants that infiltrate fungus‐farming ant societies and live with their hosts their entire lives. The present study examined whether host foraging in parasitised colonies shifts towards nutritional requirements of the parasitic guest ants as inferred from the parasite's elemental content (%C, %N, and C:N). Laboratory feeding experiments with nutritionally defined diets indicated that S. amabilis ants harvest protein‐biased substrate, and more total substrate when hosting M. symmetochus relative to when provisioning their fungus gardens and nestmates. Field surveys further showed that parasitised colonies incur reductions in fungus garden nutritional quality and quantity, brood mass, and host worker body condition. And yet these costs appear manageable across growing seasons, as parasitised fungal cultivars appear to provide sufficient nutrition for stable populations of host ants. The approach developed here shows how behavioural strategies for nutrient regulation can extend beyond the needs of the individual to entire fungus‐farming systems, and implies that S. amabilis dynamically adjusts collective foraging strategies when parasitised to enhance long‐term symbiotic stability.

Megan A Martinez  Eric J Baack  Stephen M Hovick  Kenneth D Whitney. 2018. Annals of Botany, mcy028, DOI:10.1093/aob/mcy028

Abstract

Genome size is hypothesized to affect invasiveness in plants. Key evidence comes from a previous study of invasive eastern North American populations of the grass Phalaris arundinacea: invasive genotypes with smaller genomes had higher growth rates, and genome sizes were smaller in the invasive vs. native range. This study aimed to re-investigate those patterns by examining a broader range of North American populations and by employing the modern best-practice protocol for plant genome size estimation in addition to the previously used protocol.

Paul D Blischak, Julia Chifman, Andrea D Wolfe, Laura S Kubatko. 2018. Systematic Biology, syy023, DOI:10.1093/sysbio/syy023

Abstract

The analysis of hybridization and gene flow among closely related taxa is a common goal for researchers studying speciation and phylogeography. Many methods for hybridization detection use simple site pattern frequencies from observed genomic data and compare them to null models that predict an absence of gene flow. The theory underlying the detection of hybridization using these site pattern probabilities exploits the relationship between the coalescent process for gene trees within population trees and the process of mutation along the branches of the gene trees. For certain models, site patterns are predicted to occur in equal frequency (i.e., their difference is 0), producing a set of functions called phylogenetic invariants. In this paper we introduce HyDe, a software package for detecting hybridization using phylogenetic invariants arising under the coalescent model with hybridization. HyDe is written in Python, and can be used interactively or through the command line using pre-packaged scripts. We demonstrate the use of HyDe on simulated data, as well as on two empirical data sets from the literature. We focus in particular on identifying individual hybrids within population samples and on distinguishing between hybrid speciation and gene flow. HyDe is freely available as an open source Python package under the GNU GPL v3 on both GitHub (https://github.com/pblischak/HyDe) and the Python Package Index (PyPI: https://pypi.python.org/pypi/phyde).