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1. Mistletoe distributions and abundance in the forest canopy are vulnerable to climate change.

   Trang, Kenneth; Wilson, Carol A. (July 2022, Botany 2022)

   Mistletoes are branch parasites of trees and shrubs, and keystone species found world-wide that have diverse biotic interactions with seed dispersers, pollinators, and animals that use mistletoes for shelter. They also restructure ecological communities, increasing productivity and biotic diversity. Given their important roles within their communities, a better understanding of their correlations with contemporary and predicted future climates will facilitate our understanding of the challenging aerial landscapes they inhabit. Currently mistletoe occurrence is largely attributed to host preference and availability, even though most mistletoes have many host trees and generally host tree ranges are greater than those of their mistletoes. Using Australian occurrence records and climate data with statistical analyses and modeling, we investigated correlations between climatic variables and mistletoe species distribution, richness, and predicted contemporary and future habitat suitability. Distributions of Australian mistletoe revealed differences among haustorial type and in some cases also genera and showed that ancestral haustorial types were associated with mesic ancestral habitats while derived types were generally associated with drier habitats that are considered derived within Australia. We found significant correlations with a suite of climatic variables, especially but not exclusively precipitation and temperature variables. We conclude that mistletoe distributional patterns, especially when haustorium type is considered, are correlated with climate, similar to other angiosperms. Mistletoes are vulnerable to the warmer, drier climates predicted for Australia and are expected to lose suitable habitat, primarily in interior arid regions of Australia. Ranges of species currently in northeastern tropical and subtropical regions will contract further north while those in semi-arid and arid regions are predicted to mostly shift south and southwest into temperate, montane, and Mediterranean habitat types. 

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2. Exposing the error hidden in plain sight: A critique of Calder's (1983) group selectionist seed‐dispersal hypothesis for mistletoe “mimicry” of host plants

   https://doi.org/10.1002/ece3.10760  

   Harms, Kyle E.; Watson, David M.; Santiago‐Rosario, Luis Y.; Mathews, Sarah (November 2023, Ecology and Evolution)

   Some mistletoe species (Loranthaceae) resemble their host plants to a striking degree. Various mechanisms have been proposed for the developmental origins of novel traits that cause mistletoes to appear similar to their hosts, as well as for the adaptive phenotypic evolution of such traits. Calder (1983) proposed a logically flawed group selectionist seed‐dispersal hypothesis for mistletoes to resemble their hosts. Calder's (1983) hypothesis does not provide a viable potential explanation for mistletoe resemblance to hosts. 

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3. Ecological niche modeling of Australian Loranthaceae mistletoes using a novel haustorial perspective

   Trang, Kenneth; Wilson, Carol A. (July 2021, Botany 2021)

   Mistletoe spatial patterns are poorly understood on a macroecological scale. Previous research conducted at the family-level on Loranthaceae from Australia demonstrated that unlike most plants, mistletoe species richness patterns do not correlate significantly with water and energy input. However, field studies suggested a relationship between the structure of the host-parasite union (haustorium) and environment. We hypothesize that haustorial type influences relationships between the abiotic environment and mistletoe spatial patterns. To investigate this hypothesis, we constructed ecological niche models for individual haustorial types. We have previously compared the distributions of haustorial types in both geographic and environmental space using geographic mapping and PCA, respectively. Here, we expand on our study by examining species richness, constructing predictive models, and emphasizing habitat types. Using the haustorial specimen collection housed at the UC Herbarium and relevant literature, we identified the haustorial type of 55 of the 73 Australia Loranthaceae mistletoe species. Using geographic distributional data from the Atlas of Living Australia and environmental data from WorldClim, we plotted haustorial groups in both geographic and environmental space, compared clusters in principle component space, and calculated Hutchinsonian niche overlap. We used regression to analyze the relationship between species richness and environmental variables at the haustorial level. Lastly, we constructed maximum entropy models to estimate the probability of occurrence of each haustorial group, analyzing the relative contributions of each variable to each model. We discovered that haustorial type is relatively conserved among the Australian Loranthaceae mistletoe genera, with seven out of nine genera exhibiting one haustorial type. Species with epicortical roots (ER), the ancestral character, are exclusively associated with coastal regions while those with derived haustorial types occur across the continent, including desert regions. Environmental analyses confirmed that species with ER are found in regions with milder temperatures and higher precipitation than derived types. Species richness patterns of some haustorial types, including ER, are significantly correlated with most environmental variables, while derived haustorial types are not. Maxent models for species with ER haustoria predict the highest probability of occurrence for coastal regions, while models constructed for derived types feature less bias for coastal regions. Our models demonstrate that relationships between the abiotic environment and mistletoe spatial patterns depend in part on the haustorial type. Hypotheses proposed to explain relationships between abiotic constraint on distribution and haustorial type include differences in water uptake efficiency, exposure of haustoria to the environment, longevity of haustoria, and host preference of species. 

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4. Diversification and Colonisation in the Indo‐Australian Archipelago: Genomic Insights From Colubrid Snakes

   https://doi.org/10.1111/jbi.70202  

   Bernstein, Justin M; Austin, Christopher C; Soto‐Centeno, J Angel; Huang, Tianqi; Roberts, Jackson R; McGuire, Jimmy A; Iskandar, Djoko T; Iova, Bulisa; Frederick, Jeffrey H; Sanguila, Marites B; et al (April 2026, Journal of Biogeography)

   ABSTRACT AimThe Indo‐Australian Archipelago (IAA) is one of the most geologically complex and species‐rich regions on Earth. However, our knowledge of the geological processes and dispersal mechanisms that generate archipelago‐wide distributions across the IAA is limited to a few vertebrate groups and often solely attributed to Plio‐Pleistocene sea‐level fluctuations. In this study, we use phylogenomics‐based analyses to investigate two speciose and closely related genera of snakes,LycodonandStegonotus(Serpentes: Colubridae), which are widely distributed across the IAA to identify which biogeographic and environmental processes have shaped snake diversity in this region. LocationSouth Asia and the Indo‐Australian Archipelago (Indochina, Sundaland, Philippines, Wallacea, Australasia). TaxonSnakes (Colubridae:Lycodon, Stegonotus). MethodsWe inferred a phylogeny using a genomic dataset consisting of ultraconserved elements, anchored hybrid enrichment loci, and protein‐coding genes (~5400 nuclear loci) from 38 species (154 samples) ofLycodonandStegonotus. We used ancestral range estimation analysis to identify dispersal patterns across the IAA. Additionally, we implemented ensemble species distribution models to identify potential hotspots ofLycodonandStegonotusspecies richness and determined the environmental influence on geographic distributions and species diversity. ResultsWe find that these snakes comprise six deeply divergent lineages (genera) that initially originated in Mainland Southeast Asia during the Oligocene. Diversification of these lineages is influenced not by Plio‐Pleistocene sea‐level fluctuations but by multiple historical processes, including in situ diversification, island hopping, long‐distance rafting, possible microcontinental block drifting, Cenozoic land bridge migrations and founder events. The species distribution models do not consistently estimate lower or higher species richness in any particular region within the IAA, but precipitation overall is considered an important factor in estimated species richness. Main ConclusionAlthough Plio‐Pleistocene sea‐level fluctuations are notorious species pump diversification paradigms in the IAA, multiple and more ancient geological processes and environmental factors contributed to current diversity levels and distributions. Our approach expands future investigations of alternative hypotheses of biodiversity sources in the IAA and greatly expands the diversity of causal mechanisms for discussions of terrestrial Southeast Asian biodiversity beyond dispersal versus vicariance hypotheses. 

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5. Susceptibility to parasitism by the mistletoe Phoradendron quadrangulare (Kunth) Griseb on its host Guazuma ulmifolia Lam may increase with host size

   https://doi.org/10.1016/j.fooweb.2023.e00327  

   Santiago-Rosario, Luis Y.; Espinoza-Espinoza, Nicole; Gómez, Quimey; Martínez de Zorzí, Victoria; Ramírez-Ortiz, Ramón A.; Rodríguez, Karla (December 2023, Food Webs)

   Host-parasite interactions and host susceptibility are key traits in understanding trophic energy transfer, nutrient movement and general macro-ecoevolutionary dynamics of mistletoe systems and plant-plant interactions. This research investigates host susceptibility and size-dependent interactions of the mistletoe Phoradendron quad- rangulare, a widely distributed species, on Guazuma ulmifolia. We studied the interplay between mistletoe load and host tree size, while also exploring the allometric relationship between host branch size and mistletoe size. A field surveys on 67 trees revealed varying mistletoe loads, with most trees showing no occurrence of P. quadrangulare. Parasitized trees had significantly larger diameters at breast height (DBH) than non-parasitized trees. The susceptibility of host trees to mistletoe parasitism increased with increasing DBH, indicating a positive relationship between host size and mistletoe prevalence. Furthermore, mistletoe stem diameter was found to be influenced by the diameter of the host branch suggesting that larger host trees provide more substrate for larger-sized parasites and surface area for mistletoe colonization, potentially contributing to the parasite’s survival and prevalence. This study also highlights the importance of host size in mistletoe presence and performance and provides insights into the broader eco-evolutionary dynamics and conservation strategies needed to conserve mistletoes, an often-underappreciated keystone taxa. 

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