• All 1420 offspring samples contained enough DNA to
successfully amplify 7 – 13 loci and 1208 samples were unique. Only predated
eggshell fragments resulted in duplicates of one another.
• We found all offspring matched their putative mothers with the exception of 26 eggs found in 10 clutches that were the result of intraspecific nest parasitism.
• Thirty-six sampled males were identified as fathers (24 captured males, 10 males sampled via molted feathers, and two males sampled as offspring in previous years; age 2 and 3 when they fathered offspring). These 36 males fathered completely, or in part, 63 (33.2%) of the sampled clutches. Unsampled males fathered the remaining clutches (n = 127, 66.8%). The most clutches that any given male fathered during the course of the study was seven (one male) over three years and the most fathered in a given year was three (n = 5 males). Nine unsampled males fathered more than one clutch. None of the known males that fathered offspring were yearlings. Of the 34 males with known lek affiliations, nine sired offspring of females never observed attending their lek. In two of these instances, females were observed on the closest neighboring lek to where males were displaying, but in one case, the female was only observed on a lek 54 km away. Thirteen of 14 males that fathered multiple clutches mated with females that were observed to attend the leks on which these males displayed.• Percentage of genetically identified males in the
population fathering offspring in a given year ranged from 14.3 to 54.5%, with
an overall average of 45.9%
• Of the 191 clutches, 169 (88.5%) had a single father,
13 (6.8%) had two fathers, seven (3.7%) were a mix of eggs belonging to the
putative mother with a single father and dumped eggs (single paternity in both
clutches), one (0.5%) had two fathers of different species (sage-grouse and
sharp-tailed grouse [Tympanuchus phasianellus jamesi]), and one
(0.5%) was a mix of eggs belonging to the putative mother with two fathers and
dumped eggs with single paternity.
• One hundred and thirty offspring (10.8%) came from
clutches with multiple fathers. In clutches with two fathers, paternity by
individual males ranged from 11 to 89%.
• Of the 1206 eggs, 574 (47.6%) successfully hatched.
One-hundred and four females laid 191 clutches. Each female produced between
one and six clutches with a maximum of 44 offspring and 32 successful offspring. Twenty-four females laid two sampled clutches in a single year,
with most of these clutches fathered by two different males.
Thirty-seven females laid two or more clutches over their sampled lifetime,
with most of clutches singly fathered by different males.
ª Opportunity for selection - We found that the opportunity for selection was higher
among males than females and was generally highest when measured in terms of
successful (hatched) offspring. We calculated IM for
behavioral studies that published raw copulation data (how many times every
male on a lek(s) bred over a season) for sage-grouse across the species’ range
and compared these values to our clutch values (IM = 3.9). Annual IM was high
for large leks in southeastern Wyoming (8.7 – 20.3; Wiley 1973), central
Wyoming (6.8 – 16.2; G. L. Patricelli and A. H. Krakauer, unpubl. data) and
Montana (6.0; Lumsden 1968). IM was
considerably lower in California (3.0; R. M. Gibson pers. comm.), Alberta (5.1;
J. Carpenter, unpubl. data) and for Gunnison sage-grouse in Colorado (annual IM = 2.9 –
9.9; J. Stiver, unpubl. data).
Conservation Implications