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GROW'IH, REPRODUCTION, AND LIFE
HISTORY FEATURES OF FOURWING
SALTBUSH GROWN IN A COM:MON
GARDEN
B. K. Pendleton
D. C. Freeman
E. D. McArthur
R. L. Pendleton
The :reproductive biology of diclinous plant species, species having more than one sexual morph, is of considerable research interest. Differences in the reproductive
biology of the sexual morphs may, in turn, influence the
relative allocation of resources to growth, reproduction,
and maintenance. If, as first proposed by Darwin (1877),
females allocate a greater portion of resources to reproduction than do males, and if resources are finite, then an
increase in reproductive costs should result in a decrease
in resources available to current growth as well as future
growth and reproduction (Agren 1988; Freeman and others 1976; Horvitz and Schemske 1988; Lloyd and Webb
1977; Putwain and Harper 1972; Willson 1979).
In this common garden study, life history features and
possible secondary sex characteristics were examined using
fourwing saltbush (/!triplex canescens), a species which exhibits three genotypic gender states: staminate, pistillate,
and a labile hermaphroditic genotype (Barrow 1987;
McArthur 1977; McArthur and Freeman 1982). The
common garden permits examination of the biology of
each sexual morph without the confounding effects of
differences in age structure and habitat found in natural
populations. The following questions were addressed:
kept moist through periodic misting. The resulting ramets
were planted at the Rush Valley experimental garden in
spring 1982. Ten ramets from each clone were planted in
both irrigated and control portions of the garden. All
clones had the same relative position in both the control
and treatment portions. Ramets were planted 2.4 meters
apart. All plants were watered during 1982 to aid in establishment. Plants in the irrigated portion received an
additional5 liters of water per month during the 1983
growing season.
In August of 1983, the following data were recorded for
allramets:
•
•
•
•
•
•
Mortality.
Height.
Crown diameter.
Branch length-five branches per ramet.
Sexual phenotype-male, female, or hermaphrodite.
Number of inflorescences.
• Length of five randomly selected inflorescences.
• Number of flowers per inflorescence-determined microscopically for two inflorescences from each of four flowering ramets.
• Do the sexual morphs differ in intensity of flowering
or inflorescence structure?
• Are there differences between the sexual morphs in
growth and habit?
• Are the responses to irrigation treatment equal
among the sexual morphs?
• Are there population differences in growth, reproduction, and response to treatment?
Table1-1982·83 mortality and flowering percentages of cloned
ramets from Spanish Fork and Kingston Canyon
populations
Females
Mortality
Spanish Fork ramets
Irrigated
Control
METHODS
Stem cuttings of male, female, and hennaphrodite plants
from two contrasting tetraploid populations, Spanish Fork
Canyon and Kingston Canyon, were rooted in peat pellets
Kingston Canyon ramets
Irrigated
Control
Flowering
Spanish Fork ramets
Irrigated
Control
Poster paper presented at the Symposium on Ecology, Management,
and Restoration of Intermountain Annual Rangelands, Boise, ID,
May 18-22, 1992.
B. K. Pendleton is Ecologist, E. D. McArthur is Supervisory Research
Geneticist, and R. L. Pendleton is Ecologist at the Shrub Sciences Laboratory, Intermountain Research Station, Forest Service, U.S. Department of
Agriculture, Provo, UT. D. C. Freeman is Associate Professor, Department
of Biological Sciences, Wayne State University, Detroit, MI.
Kingston Canyon ramets
Irrigated
Control
136
Males Hermaphrodites
-----------Ps~nt----------2.0
8.0
10.0
7.5
4.5
4.0
6.1
5.4
6.7
8.3
8.0
17.0
93.8
76.3
97.2
94.6
85.7
85.7
58.7
72.1
89.3
87.3
72.8
80.8
MORTALITY
Kingston Canyon Population-Male ramets had the
smallest growth measures (table 3). Females were consistently larger than males. The few exceptions to these
trends, irrigation height and crown diameter, were nonsignificant. Hermaphrodite ramets were most like female
with the exception of the height per crown (HPC) ratio,
which was nonsignificant.
There were no significant differences between sexual
morphs for height, crown diameter, and HPC measures in
the irrigation environment. Irrigation treatment produced
an increase in height and crown for all sexual morphs, and
an increase in branch length of male ramets. Hermaphrodites and females responded to the irrigation treatment
similarly.
Mortality, both between the sexes and between the
populations, was quite uniform, with the exception of KC
hermaphrodite clone three (table 1). Most mortality was
attributable to factors other than sexual morph (for example, transplant shock and herbivory). The likelihood
that a sexual morph would flower, males being most
likely, hermaphrodites next most likely, and females least
likely, was approximately the same in both populations.
Kingston Canyon and Spanish Fork Canyon ramets did
not have a similar response to irrigation treatment.
Spanish Fork females showed a positive response to irrigation; Kingston Canyon females showed a negative response. Spanish Fork ramets, regardless of sexual morph,
flowered with greater frequency than Kingston Canyon
ramets.
REPRODUCTION
Spanish Fork Population-Female ramets on average had longer but fewer inflorescences than did male
ramets (table 2). Hermaphrodite inflorescences were intermediate in length. Flowers per inflorescence did not
vary significantly between sexual morphs in either environment. Male and female ramets increased the number
of inflorescences under irrigation; males by 81 percent
and females by 33 percent. Hermaphrodite ramets, which
had the greatest number of inflorescences in the control
environment, were unaffected by irrigation.
GROWTH
Spamish Fork Population-Male ramets had the
smallest mean values for all growth measures (table 2).
Female ramets were consistently larger than male. Hermaphrodite ramets were intermediate in most cases, with
a significantly larger crown diameter in the control environment. Hermaphrodite ramets were most like female
in growth pattern. Irrigation treatment produced an increase in all growth measures. Males and females responded to the irrigation treatment in a similar manner.
Kingston Canyon Population-Hermaphrodite ramets
had the longest inflorescences and the most flowers per
Table 2-Mean values of the growth and reproduction measurements for the Spanish Fork Canyon population. All
length measurements are in millimeters. Means followed by the same letter are not significant at the 0.05 level
Trait
Sexual
morph
Control
environment
Irrigation
treatment
Population
mean
Height
Female
Male
Hermaphrodite
311.85 a
240.14 b
297.18 a
370.94a
289.44c
340.91 b
341.86
264.45
320.63
Crown diameter
Female
Male
Hermaphrodite
316.57 b
292.79b
355.60a
421.20 a
383.61 a
382.86a
369.71
337.58
370.21
Branch length
Female
Male
Hermaphrodite
71.00 a
28.70c
45.38b
79.33a
32.19 c
53.87b
75.28
30.54
49.93
Height per
crown ratio
Female
Male
Hermaphrodite
1.03a
.83b
.88b
.96a
.nb
.93a
.99
.80
.91
Number of
inflorescences
Female
Male
Hermaphrodite
37.15 b
44.21 b
59.52a
49.57b
80.21 a
60.25b
44.09
62.21
59.92
Inflorescence
length
Female
Male
Hermaphrodite
34.63a
13.54c
21.92 b
36.15 a
15.70c
28.87b
35.48
14.64
25.80
Flowers per
inflorescence
Female
Male
Hermaphrodite
75.14a
86.84a
87.70a
86.11 a
87.34a
102.63 a
80.58
87.89
95.74
137
Table 3-Mean values and standard deviations of the growth and reproduction measurements for the Kingston Canyon
population. All length measurements are in millimeters. Means followed by the same letter are not significant
at the 0.05 level
Sexual
morph
Control
environment
Irrigation
treatment
Population
mean
Height
Female
Male
Hermaphrodite
320.71 a
243.20b
292.71 a
336.57 a
320.45a
311.79a
328.85
282.17
303.35
Crown diameter
Female
Male
Hermaphrodite
323.92a
262.04b
299.73ab
375.36a
384.64a
361.04 a
350.32
323.89
333.91
Branch length
Female
Male
Hermaphrodite
79.69a
43.84b
76.22a
78.80a
67.66b
74.13 ab
79.22
55.83
75.05
Height per
crown ratio
Female
Male
Hermaphrodite
.95a
.95a
1.01 a
1.05a
.86a
.90a
1.00
.91
.94
Number of
inflorescences
Female
Male
Hermaphrodite
19.73 b
53.35a
29.47b
34.41 b
68.02a
44.63b
27.32
60.84
37.76
Inflorescence
length
Female
Male
Hermaphrodite
24.11 b
16.71 c
37.28a
28.75b
19.07 c
37.87 a
26.24
17.87
37.60
Flowers per
Inflorescence
Female
Male
Hermaphrodite
93.55a
66.56a
121.68 a
84.14 b
118.35 b
168.25 a
88.97
93.82
150.87
Trait
Table 4-Percent of variance by clone (genotype) and various environmental components for Spanish Fork Canyon growth and
reproductive parameters
Sexual
morph
Female
Male
Hermaphrodite
Source
Height
Crown
diameter
Number
Inflorescences
Branch
length
Inflorescence
length
Treatment
Clone
Treatment
x clone
Ramet
Error
0
15.05
5.44
20.19
0
23.15
0.47
32.46
0.06
31.32
21.45
13.80
28.85
63.49
60.57
48.00
13.92
37.67
15.47
6.35
48.91
13.44
0
0
0
4.28
2.04
33.94
1.61
15.59
0
0
14.15
32.21
35.43
Treatment
Clone
Treatment
xclone
Ramet
Error
13.30
39.93
47.76
100.00
95.72
15.52
23.19
25.31
Treatment
Clone
Treatment
xclone
Ramet
Error
26.39
44.14
25.68
9.11
0
29.57
10.00
.21
12.56
13.76
8.16
11.21
57.05
59.22
14.n
34.65
50.38
15.26
20.06
38.36
0
0
29.47
138
inflorescence, although the difference was not always significant (table 3). Female ramets had longer but fewer inflorescences than did male ramets. All three sexual morphs
increased the number of inflorescences under irrigation.
Male and hermaphrodite ramets also increased the number of flowers per inflorescence.
and Spanish Fork populations. Growth and reproduction
trends of the sexual morphs were also similar, but less
pronounced in the Kingston Canyon population. The unusually high precipitation experienced during the 1982
and 1983 growing seasons created relatively lush conditions for the more xeric KC plants, minimizing differences
between sexual morphs.
4. Irrigation treatment accounted for over four times
the variation in hermaphroditic plants as it did for either
male or female plants. This observation is consistent with
the hypothesis that hermaphrodites are better able to
respond to environmental change than either males or
females.
VARIANCE PARTITIONING
Mean squares values from the ANOVA were partitioned
into their variance components following Bulmer (1980).
Sexual morphs differed markedly in the variation percentage accounted for by each source. For example, the clone
term for number of inflorescences accounts for 23.15 percent of the variation in female clones, 4.28 percent of the
variation in male clones, and 29.57 percent of the variation
in hermaphrodite clones. Irrigation treatment accounted
for a small percentage of the variation in male and female
clones (an average of 5.1 percent and 1.9 percent, respectively), but accounted for an average of20.7 percent of the
hermaphrodite variance (table 4).
The clone term was significant across all variables and
sexes, and accounted for a significant fraction of the total
variation in all cases, indicating a high degree of genetic
variation within the Spanish Fork Canyon population. The
high percentage of variance accounted for by the ramet
term of the analysis indicates that substantial microenvironmental variation can occur across relatively short distances within the common garden.
REFERENCES
Agren, J. 1988. Sexual differences in biomass and nutrient allocation in the dioeciousRubus chamaemorus.
Ecology. 69:962-973.
Barrow, J. R. 1987. The effects of chromosome number on
sex expression in Atriple% canescens. Botanical Gazette.
148: 379-385.
Bulmer, M. G. 1980. The mathematical theory of quantitative genetics. Oxford: Clarendon Press. 255 p.
Darwin, C. 1889. The different forms of flowers on plants
of the same species. New York: D. Appleton and Company. 352p.
Freeman, D. C.; Klikoff, L. G.; Harper, K. T. 1976. Differential resource utilization by the sexes of dioecious
plants. Science.193: 597-599.
Horvitz, C. C.; Schemske, D. W. 1988. Demographic cost
of reproduction in a neotropical herb: an experimental
field study. Ecology. 69: 1741-1745.
Lloyd, D. G.; Webb, C. J. 1977. Secondary sex characters
in seed plants. Botanical Review. 43: 177-216.
McArthur, E. D.1977. Environmentally induced changes
of sex expression in Atriple% canescens. Heredity. 38:
97-103.
McArthur, E. D.; Freeman, D. C. 1982. Sex expression in
Atriplex canescens: genetics and environment. Botanical
Gazette. 143:476-482.
Putwain, P. D.; Harper, J. L. 1972. Studies in the dynamics of plant populations. V. Mechanisms governing sex
ratio in Rumex acetosa and Rumex acetosella. Journal of
Ecology. 60: 113-129.
CONCLUSIONS
1. Differences between sexual morphs in growth and
flowering schedules suggest tradeoffs in resource allocation
between growth and reproduction. Males flowered with
the greatest frequency and intensity, while producing the
smallest growth parameters. Females had the largest
measures of vegetative growth and flowered with the least
frequency and intensity.
2. Hermaphroditic plants have a growth and reproductive biology distinct from males and females. Values were
most like females in growth, but more like males in intensity of flowering. Hermaphrodites have the largest number of flowers per inflorescence.
3. Mean values for growth and reproductive characters
examined were quite similar between the Kingston Canyon
139