Mason Kulbaba
Research
Offspring Quality and the Capacity for Adaptation
Instances of rapid adaptation to a variable and changing environment have been amply documented. Whereas most studies of adaptation take a retrospective approach to explain past adaptation, recent studies have employed Fisher’s Fundamental Theorem of Natural Selection to prospectively predict changes in fitness across generations. Generally, there is agreement that population-level estimates of genetic variation (e.g., additive genetic variance for fitness), the raw material for natural selection, provides insights into how fitness may change across generations. However, studies that even take prospective approaches to predicting changes in fitness rely exclusively on overall number of progeny produced by individuals or individual families (e.g., absolute fitness). Whereas these studies have advanced our understanding of the adaptive process, absolute fitness does not account for variation in offspring quality. This overlooked aspect of individual fitness directly affects fitness contributions of individual lineages and population viability through the varying survival and reproductive performance of offspring. Given the span of potential mating outcomes (see below Plant Mating Portfolios), offspring would span a continuum in the magnitude of inbreeding and inbreeding depression (e.g., negative fitness effects of inbreeding). Consistent inbreeding increases the probability of expressing deleterious recessive alleles through increased homozygosity and/or reduces the benefits of heterosis. Offspring quality could be realized across the sequence of life-history stages. For example, successful development of embryos to seeds and subsequent dispersal, germination, growth, and reproduction. Relative performance among individuals at each life-history stage would depend on the magnitude and timing of the expression of inbreeding depression. Whereas early acting inbreeding depression can efficiently purge deleterious alleles and maintain mean offspring quality, deleterious alleles in individuals experiencing late-acting inbreeding depression may be more persistent. Regardless, heterogeneity in the severity and timing of inbreeding depression across life-history events creates diverse opportunities for selection across a continuum of mating outcomes. Despite the evolutionary opportunities and importance of offspring quality, almost nothing is known beyond the impacts of the basic quantity-quality tradeoff.
Relevant publications
Shaw, R. G., C. J. Geyer, M. W. Kulbaba, S. N. Sheth, V. M. Eckhart & R. E. Pain (2026) Realization of ongoing evolutionary adaptation in the field. Evolution Letters 10: 315-325.
Kulbaba, M. W., Yoko, Z., and J. Hamilton. 2023. Chasing the fitness optimum: temporal variation in the genetic and environmental expression of life-history traits for a perennial plant. Annals of Botany. 132: 1191–1204. PDF
Kulbaba, M. W., Sheth, S. N., Paine, R. E., Eckhart, V. M., Shaw. R. G. 2019. Additive genetic variance for lifetime fitness and the capacity for adaptation in an annual plant. Evolution 73: 1558-5646. PDF.
Sheth, S. N., Kulbaba, M. W., Pain, R. E., and R. G. Shaw 2018. Expression of additive genetic variance for fitness in a population of partridge pea grown in two field sites. Evolution 72: 2537-2545. PDF
Plant Mating Portfolios
Pollen dispersal by vectors typically results in nonrandom promiscuous mating within a local neighborhood which favours hermaphroditism (e.g., bisexual or perfect flowers), the most common sexual system among flowering plants. Hermaphroditism introduces the opportunity for self-fertilization. Therefore, local mating neighbourhoods may lead to varying degrees of genetic outcome (e.g., complete selfing to complete outcrossing) and relatedness (e.g., entirely full or half siblings as extremes) in offspring. The occurrence of mating between individuals of varying relatedness (e.g., biparental inbreeding) further diversifies the distribution of offspring genotypes, contributing to heterogeneous genetic structuring of populations. Such genetic heterogeneity can be further reinforced when animal pollinators have a preference for specific traits (e.g., floral trait or nectar properties), facilitating assortative mating. These diverse mating patterns result in a myriad of complex and dynamic mating outcomes that can be quantitatively described by an individual’s mating portfolio, namely, the number or proportion of offspring resulting from different mating types. In addition, the mating portfolio could include features of mates that influence offspring quality. For example, mates may differ in their relatedness, with consequences for offspring inbreeding depression. Finally, the diversity of mates may confer reproductive advantages, and therefore be under selection. For example, multiple pollen donors increase the opportunity and intensity of pollen-tube competition and female mate choice, and reduce the probability of mating with incompatible or poor-quality mates that produce offspring with a poor genetic fit for an established environment.
Relevant publications
Harder, L. D. and Kulbaba, M. W. (2026) The richness, frequency and relatedness components of mate diversity and mate portfolios. New Phytologist 251: 3703-3713.
Kulbaba, M. W. and L. D. Harder. (2025) A SNP-based approach to estimating the mating and relatedness components of plant mating portfolios. Botany 103: 1-9.
Systematic Patterns of Subindividual Trait Variation
The interaction between plants and their environments during reproduction is made more complex by the production of similar but not identical flowers within a single floral display. The production of multiple flowers within a single display allows for trait variation among flowers, often in predictable patterns (e.g., decrease in flower size from lower to upper positions). The extent to which these patterns functionally contribute to fitness and differ among individuals is unknown. Through genetic-marker based estimates of quantitative genetic parameters, and function-valued trait analyses, my work provided the first progress in assessing the heritability, evolvability, and selection that maintains systematic patterns of subindividual variation. My findings determined that patterns of within-individual variation have a genetic basis and exhibit substantial estimates of evolvability. Therefore, these patterns may respond rapidly to selection. Finally, both the direction and magnitude of selection changes across flowering times, further highlighting the complexity of the interaction between dynamic plant phenotypes and the environment.
Relevant publications
Arteaga, G. and Kulbaba, M. W. (Revision in review). Within-individual floral variation and the dynamic morphology of Vicia americana (Fabaceae) reproductive phenotypes.
Harder, L.D., Strelin, M.M, Clocher, I.C, Kulbaba, M.W. and M. A. Aizen. 2019. The dynamic mosaic phenotypes of flowering plants. New Phytologist 224: 1021-1034. Special issue: The ecology, evolution, and genetics of plant reproductive systems. PDF
Kulbaba, M. W., Clocher, I. C., and L. D. Harder. 2017. Inflorescence characteristics as function-valued traits: analysis of heritability and selection on architectural effects. Journal of Systematics and Evolution 55 (6) 559 – 565. Invited for special issue on inflorescence displays. PDF.