Final answer:
In haplodiploid systems, selection on males should be directional, as they are haploid and any genetic factor benefiting their mother's or their own reproductive success is favored. For sperm-depleted males, this translates to an optimized mating strategy, such as choosing larger, more fecund females to ensure reproductive success with limited resources.
Step-by-step explanation:
In haplodiploid systems, sons are haploid, indicating that they inherit only one set of chromosomes from their mother and have no father. Because sons are produced from unfertilized eggs, they cannot have sons themselves and have unrestricted access to their mother's genes. This means that any genetic factors that enhance their mother's likelihood of producing more sons is indirectly selected for. In the context of sexual selection, it implies that selection acting on males should be directional, favoring traits that increase their mother's or their own reproductive success.
In cases like sperm-depleted males, this can translate to behavioral changes. For instance, sperm-depleted males might prefer mating with larger, more fecund females as these females have a higher fertility potential, thus optimizing the chances of success given their limited sperm resources. This leads to selective pressures that could reinforce the preference for traits that are advantageous under the conditions of limited sperm, such as preferring large, fecund females, thereby increasing the efficiency of a limited reproductive resource: sperm.