J. Phil Gibson

DIFFERENCES IN SHADE TOLERANCE HELP EXPLAIN VARYING SUCCESS OF TWO SYMPATRIC ALNUS SPECIES

Alnus maritima and Alnus serrulata are riparian shrubs that occur in similar habitats in the southern and eastern United States. Alnus serrulata is abundant throughout this range, but A. maritima is rare, occurring only in small populations in Oklahoma and Georgia and on the Delmarva Peninsula. Alnus maritima is more resistant than A. serrulata to water and temperature stresses, but the degree to which insolation influences the restricted distribution of A. maritima is unknown. Our goals were to characterize the shade tolerance of A. maritima and A. serrulata and determine whether differences in shade tolerance could help explain the differing ecological success of the two species. Measurements in nature showed that leaves of A. serrulata have greater concentrations of chlorophyll than do leaves of A. maritima, and a greater percentage of A. serrulata inhabit shaded sites. Two experiments evaluating the resistance of seedlings to light‐deficit stress revealed that A. maritima had a greater photosynthetic capacity and grew more quickly than A. serrulata in full sunlight. In shade, survival of seedlings was lower and reductions in photosynthesis and growth were greater for A. maritima than for A. serrulata. We conclude that A. serrulata is tolerant and A. maritima is intolerant of shade. Moreover, we conclude that shade intolerance strongly restricts the potential niches of A. maritima within the region where the shade‐tolerant A. serrulata is comparatively abundant.

Population genetic diversity and structure within and among disjunct populations of Alnus maritima (seaside alder) using microsatellites

Small, isolated populations are prone to genetic drift and high levels of inbreeding that can threaten their long-term survival. Alnus maritima persists exclusively in three groups of small, highly disjunct, regional populations in the Delmarva Peninsula, Georgia, and Oklahoma. Trees in the three regions are recognized as separate subspecies. Microsatellite markers were used to measure fine-scale population genetic diversity and structure (1) within and among regions and (2) within and among populations in each region. Compared to a previous study utilizing allozymes, microsatellite data show higher levels of variation, lower levels of inbreeding, but similar levels of genetic differentiation among regions. Significant genetic differentiation was detected among regions and among distinct populations within regions. Genetic differentiation was significantly correlated with geographic distance among regional populations, but not among populations within regions. Populations, therefore, likely represent fragments of formerly extensive networks of populations that have decayed and retracted due to competition with other species better adapted to the shadier habitats of late-succession environments. The unique genetic features of populations within different regions should be considered as part of future conservation efforts.

Development and characterization of nineteen polymorphic microsatellite loci from seaside alder, Alnus maritima

We isolated and characterized 19 microsatellite loci from the endangered seaside alder, Alnus maritima. Loci were screened in 24 individuals of A. maritima and four individuals of its congener the hazel alder, A. serrulata. The number of alleles per locus ranged from 2 to 6, observed heterozygosity ranged from 0 to 0.952, and the probability of identity values ranged from 0.126 to 0.850. These new loci provide tools for characterizing the population genetics of this rare tree.

Correlations Between Tree Thinking and Acceptance of Evolution in Introductory Biology Students

BackgroundTree thinking refers to an approach to evolution education that emphasizes reading and interpreting phylogenetic trees. We studied the relationship between introductory biology students’ tree-thinking ability and their acceptance of evolutionary theory.ResultsComparisons between a semester in which interpretation of phylogenetic trees and related concepts were taught as stand-alone topics versus one in which tree thinking was used as an organizing framework for the course curriculum found significant increases in students’ ability to read and interpret trees in both semesters, but only in the tree thinking semester was there a significant increase in students’ scores on the Measure of the Acceptance of the Theory of Evolution (MATE) instrument. Over four additional semesters, the Tree Thinking Concept Inventory (TTCI) was used to assess students’ tree-thinking abilities before and after the course. We found that MATE posttest scores correlated with gains in tree-thinking ability. These increases in MATE posttest scores were predominantly due to students’ reporting greater acceptance of the scientific evidence supporting evolutionary theory.ConclusionsIncreased acceptance of evolution in a tree-thinking versus non-tree-thinking semester and significant positive correlations between TTCI and MATE scores indicate there is a relationship between tree-thinking ability and acceptance of evolution. This result suggests that, as a framework to connect different forms of data and investigate a variety of biological phenomena, tree thinking can promote greater acceptance of the evidence and scientific validity of evolutionary theory in introductory biology students.

Bet-hedging against larval herbivory and seed bank mortality in the evolution of heterocarpy

PREMISE OF THE STUDYnBet-hedging strategies maximize long-term geometric fitness at the cost of reduced arithmetic fitness by offsetting different mortality risks. Heterocarpic systems accomplish bet-hedging through the production of two or more fruit types that vary in dormancy and dispersal ability. It is unknown whether heterocarpy also offsets predispersal mortality risks. To address this question, we investigated whether heterocarpy in Grindelia ciliata (Asteraceae) also offsets mortality risks posed by a seed predator Schinia mortua (Noctuidae) to increase plant fitness.nnnMETHODSnWe conducted two manipulative experiments to quantify critical life history components of this plant-insect interaction. We measured predispersal achene mortality from herbivory, postdispersal achene mortality in the seed bank, and seedling emergence. These measurements were then used in deterministic models to evaluate evolutionary consequences of predispersal seed mortality in G. ciliata.nnnKEY RESULTSnDormant achene types were less vulnerable to herbivory but more susceptible to mortality in the seed bank due to delayed seed emergence. Nondormant achene types experienced high predispersal mortality but low seed bank mortality due to rapid germination. Our herbivore-dependent model improved fit between observed and expected proportions of dormant and nondormant G. ciliata achenes and showed that heterocarpy could evolve in the absence of postgermination mortality.nnnCONCLUSIONSnOur study provides empirical support of how predispersal herbivory can be equally important to postdispersal seed mortality risks in the evolution and maintenance of a heterocarpic reproductive system and expands understanding of how bet-hedging theory can be used to understand this unique reproductive strategy.

Botanical Phylo-Cards: A Tree-Thinking Game to Teach Plant Evolution

Abstract Students often have limited understanding of the major innovations in plant evolution. We developed a card sorting activity based on tree thinking that is suitable for students with a wide range of abilities and experience. Through this activity, students learn how scientists organize taxa into biologically meaningful, natural groups that illustrate important events in terrestrial plant evolution. The activity corresponds to several NGSS standards and is suitable for use in classroom or laboratory settings and as a public educational outreach activity. The Botanical Phylo-Card Game addresses several components of Next Generation Science Standards (NGSS Lead States, 2013) such as Inheritance/Variation in Traits (3-LS3-1, HS-LS3-1, HS-LS4-2) and Natural Selection/Evolution (MS-LS4-2, HS-LS4-1). The game involves disciplinary core ideas about biodiversity, evolution, and common ancestry; crosscutting concepts regarding identification and interpretation of patterns; and scientific practices of constructing explanations and engaging in arguments from evidence that can guide individualized implementation and assessment of the activity by different instructors.

Mating System Analysis of Alnus maritima (Seaside Alder), a Rare Riparian Tree

Abstract Effective conservation requires an understanding of the genetic interactions among populations and individuals of a species, particularly those with fragmented, isolated distributions. Alnus maritima (seaside alder) is a rare tree species with an extremely fragmented distribution of highly isolated populations in the Delmarva Peninsula, Georgia, and Oklahoma. We conducted a mating system study to estimate the outcrossing rate, inbreeding coefficient, biparental inbreeding rate, and correlation of paternity in progeny from a Georgia and an Oklahoma population to investigate the effects of isolation on the A. maritima mating system. Data from nine microsatellite loci showed similarly high multilocus outcrossing rates in both populations (tm u200a=u200a 0.94). Individual tree outcrossing rates were also high (tm u200a=u200a 0.873–1.047). There was no significant biparental inbreeding in either population, but there was significantly higher correlated paternity in the Oklahoma population. Results showed the high outcrossing expected for a wind-pollinated, monoecious species that can promote the maintenance of genetic variation detected in A. maritima seed pools and standing populations. Likewise, pollen flow among Oklahoma populations may promote maintenance of regional genetic variation. However, despite the genetic diversity in the seed pool generated by A. maritimas highly outcrossed mating system, failure of new individuals to be recruited into populations from seed presents an obstacle that will need to be considered when developing conservation strategies for this rare species.