1. Four seeds per phenotype (4R,
4r) totaling eight seeds of each
family were planted
individually in 3 ½ inch square
plastic garden pots totaling 40
seeds.
Causes and consequences of variation in seed morphology in Mimulus guttatus
Kaytlynn Marceaux
University of Kansas, Department of Ecology and Evolutionary Biology, Lawrence KS 66045
Seed quality can play an important role in the germination, development, and eventual
reproduction of plants. The simple indication of differences in quality among seeds may
be provided by seed shape. If seed shape is heritable, it could have important
consequences for the evolution of species. In the yellow monkeyflower (Mimulus
guttatus), there is striking variation in seed shape, primarily in the degree to which they
appear wrinkled. However, the relationship between seed shape and seed quality has not
previously been explored. To examine this relationship, I compare the germination and
subsequent developmental rate of different seed shapes, finding that wrinkled seeds are
less likely to germinate and take longer to reach reproductive maturity. Furthermore, the
seed shape effects certain floral characteristics, specifically the length of the pistil. I also
performed controlled crosses between plants derived from wrinkled or non-wrinkled
seeds to determine if there is a genetic basis for variation in seed shape. I find evidence
that seed shape is at least partially heritable and is particularly affected by inbreeding,
regardless of the parental seed shape. These findings may prove to be important for
natural evolution and how we characterize fitness in M. guttatus.
Modern genetics is founded on Mendel’s classic study of Round (R) vs. Wrinkled (r)
peas, in which he laid the groundwork for how genetic differences determine phenotypic
differences[3]. In addition to Mendel’s work there have been several genes found that
control seed phenotype as well as seed composition and development [1,3]. Seed
composition consists of lipids, saccharides (sugars), and protein storage and any reduction
or elevation of these components can lead to poor nutrition of seedlings which can further
lead to other detrimental effects on plant characteristics [3].
Phenotypic effects of Mimulus guttatus (yellow monkeyflower) have been shown to
influence progeny characteristics [2]. Though M. guttatus is not a pea, nor related to the
pea species, there are visible differences in their seed shape that may affect future floral
characteristic such as germination time, flower time, pistil length, and breeding. Here I
describe the various differences I observed between the two distinguished seed
phenotypes, Round vs. Wrinkled, in three different experiments.
Experiment 3
Abstract
Introduction
Acknowledgments:
I would like to thank my advisor, Dr. John Kelly, and my mentor, Patrick Monnahan for advancing my
understanding in EEB and statistical analysis.
To determine the causes of seed
morphology and the
consequences it may have on
the following
Effect of seed shape and
breeding on progeny seed
shape
Seed shape effects on certain
floral characteristics
M. guttatus seeds pictured under a dissecting microscope
Methods
Experiment 1 (Cohort
A)
Two seeds per phenotype (2R, 2r)
totaling four seeds of each family were
planted in a non-random order within
one 98 compartmental flat totaling 96
seeds. Data collected on germination
time, pistil length, and day to flower.
Collected seeds from 24
different families of an F1
generation, grown in nature
from a cross between two
genetic lines
Experiment 2 (Cohort B)
Collected seeds from 6 families
of previous 24 families. Used
four seed packets per family of
an F1 generation, grown in
nature from a cross between two
genetic lines
Each seed was identified under a dissecting
microscope based on physical
characteristics of round (R) or wrinkled (r)
Four seeds per phenotype (4R, 4r) totaling
eight seeds of each family were planted in
a random order within two 98
compartmental flats totaling 192 seeds.
Data collected on germination time, pistil
length, and day to flower.
Results cont’d
○ Round seeds are more likely to germinate (p= 0.09;
logistic regression)
○ Round seeds germinate more quickly that Wrinkled
seeds (p= 0.035; Fig. 1a; factorial ANOVA)
○ After germination, Wrinkled seeds take longer to flower
(p= 0.025; Fig. 1b; factorial ANOVA)
○ Round seeds tend to have a longer pistil length than the
Wrinkled seed (p= 0.0001; Fig. 1c; factorial ANOVA)
Each plant that successfully reached
reproductive maturity was randomly
paired, crossed, and selfed. Progeny
seeds were collected and 5 seeds
measured per plant with a
micrometer.
Fig.1: Data from Experiment 1 and 2, defined as Cohort A and B, were analyzed against each other, (a) Germination time (days) vs Cohort,
Seed Type (b) Day of Flower (days) vs Cohort, Seed Type, (c) Pistil length (mm) vs Cohort, Seed Type interval plot of the difference between
experiment 1 and 2 defined cohorts.
(a)
(b)
Results
Objective:
Germination and subsequent
developmental rate of
different seed shapes
(b)
Fig. 2: Data from experiment 3 was analyzed independently from previous experiments and is strictly based on progeny
seed morphology. (a) Interval plot of seed area (mm2
) (p = 0.0001; ANOVA), (b) Effect of Inbreeding on seed shape (p =
0.01; logistic regression), (c) Effect of parental phenotype on progeny seed shape (p = 0.0009; logistic regression)
(a)
70% of progeny were Round when
crossed between Maternal Round seeds
and Paternal Wrinkled seeds
90% of progeny were Round when
crossed between Maternal Round seeds
and Paternal Round seeds
♀ ♂
♀
50% of progeny were Round when
crossed between Maternal Wrinkled
and Paternal Round seeds
♂
♀ ♂
Discussion / Conclusions
Fig. 3: Clear growth rate differences observed between
Wrinkled (a) and Round (b) seeds in Experiment 3 of parent
population before performing crosses. Note the poor
germination and reproductive maturity in Wrinkled seeds (a).
(a) (b)
The objective of this study was to determine if there is a genetic basis for
variation in seed shape and if this variation has consequences for subsequent
germination, development, and morphology of individuals. This research
determined three consequences on the cause of seed morphology within M. guttatus.
1. Wrinkled seeds were less likely to germinate, take longer to germinate, and take
longer to flower after germination (Fig. 1a and 1b)
● The implications of slower germination and flowering rates could reduce the
probability of being cross-fertilized or simply surviving to reproduce in nature
● Since M. guttatus is an annual plant the major selective event that determines
fitness is the ability to flower before water is no longer available.
2. The pistil length of Round seeds is found to be longer than Wrinkled seeds (Fig. 1c)
● Longer pistil length may be important because M. guttatus practices cross-
fertilization as well as self-fertilization (outcrossing/inbreeding).
● A longer pistil may be easier for pollinators to access increasing the probability
of cross-fertilization.
3. Genetic basis and mating system (selfed vs crossed) found that some families
produce significantly more grapes Selfed progeny are more likely to be raisins,
which is in line with effects of deleterious recessive alleles. Maternal effects
suggested by effect of Cross Type on Seed Shape (Fig. 2).
● Maternal characteristics could be the leading cause of seed morphology which, as
we have seen, have consequences for subsequent developmental characteristics
Future research could probe the genetic basis of this trait (identify specific genes and
how they affect seed shape) to compare/contrast with peas to observe parallel or
independent evolution of seed shape.References:
1. Bhattacharyya, M.K., Smith, A.M., Ellis, T.H.N., Hedely, C., & Martin, C. 1990. “The Wrinkled-seed Character of Pea Described by Mendel is Caused by a Transposon-like
Insertion in a Gene Encoding Starch-Branching Enzyme.” Trends in Genetics 6:73. Web. 29 Mar. 2015.
2. Platenkamp, G.A.J. & Shaw, R.G. 1993. “Environmental and Genetic Maternal Effects on Seed Characters in Nemophila menziesii.” Evolution 47:540-55. Web. 28 Mar. 2015.
3. Reid, J.B. & Ross, J.J. 2011. “Mendel’s Genes: Toward a Full Molecular Characterization.” Genetics Society of America 189:2-10. Web. 28 Mar. 2015.
(c)
(c)
Collected seeds from 5 families
of previous 24 families. Each
family contributed 8 seeds of an
F1 generation, grown in nature
from a cross between two genetic
lines